I managed this with a sloop this morning and it was fairly straight forward after a bit of thinking things through. Here are some tips for someone who might want to try this.
1- I started my voyage with a sloop in Private(locked) mode. I've had too many instances where a brand new person joins my ship and sails it off into rocks or fires all my cannon balls. I'm still trying to understand the logic, but whatever. You wouldn't start a job at Burger King and immediately throw everything you see into the fryer!!! Why are you doing it on my boat?!
I want as much control over the venture as possible.
2- I stocked up on all the cannon balls, planks, and bananas I could. I hit up the started island, and the first nearest island. Bananas and planks are important here.
*Bananas* = 50 if you are a pretty terrible player (don't worry, we all sucked at some point) 20 if you know how to stay out of fire.
*Planks* = 20-30. Expect to get a hit a few times. It's going to happen.
*Cannon Balls* = 30-40. More if you are going to actively use your cannon to make kills. My strategy puts you too close to really use it effectively.
3- I found a skull fort up on the server and sailed to it. Now here is the kicker, you need to get as close as possible to the fort, but (and I've tested this), when a ship (any ship) gets close to the island, it was auto-spawn skellies at a few of the cannons. You WILL be fired upon. So, coasting in with your sail up is highly unadvised. Roll in with full sail and slam down the anchor as close to the dock as you can.
Make your ship as friendly as your can! I usually put on a black sail with a front end. Not sure what they are called off hand, but the lion looking thing. Then fly a white flag at the top. This will give players coming into the island an assumption that you know what you are doing and are not looking to fight. This doesn't always work, but it beats flying a pirate flag, which instantly tells me they are aggressive and to stay away or kill them on site.
4- Ok, you are stopped close to the dock now. If anything is firing at you, repair and wait till the cannons stop. When they do, RUN to the skelly firing at you and kill them. Your job right now is to make sure your boat is safe before you proceed.
Remember where that cannon that was firing at you is. You will need to keep an eye out for it, because you WILL have to take care of the skelly when it respawns. When it does, drop everything and kill it. #1 thing is to keep your boat alive, without it, you will fail. It will be your respawn point.
Put up your sails and de-anchor your boat. this way you and swivel the boat and fire your cannons if needed. Also, it gives you a quick get-the-hell-out move if another ship comes in being aggressive.
(((At any time someone else could come and try to claim the island. Usually, I find the Galleons do this the most. Make sure you state as soon as they are within communication distance, that you are friendly and will help them as long as treasure is divided up. Solo fighting multiple people at a skelly fort is a death-wish no matter how good you are... the entire map knows where that island is, so they will be back to take revenge and, most likely, your loot.)))
5- Now, when you first get on the island, ignore the skellies as much as possible and look for explosive barrels, set these outside the walls. If you need one later, grab it and run back in. You don't want random explosions to detonate 2-3 other barrels that you could have used. Also, look through the item barrels, taking notes of where bananas are. You don't want to run back to your ship every 2 minutes to get them, use what's on the island first. Keep an eye out for ammo crates. Make sure you have a plan to access them if things get out of hand.
6- Ok, now comes the interesting part... the waves of skellies.
Standard Skeletons (no weapons) - these usually spawn in a massive group of 12 or so. They are fast and numerous so you have to group them up first. Kite them around (run around the outside of the group to group them together), then each sword swing will hit multiple. While you swing, move backwards and side to side. Always try to keep the group in front of you. If the skellies start spreading out, run around the outside and group them up again. Rinse and repeat.
Leafy Skeletons - These will regenerate like crazy in the water (even in an inch), so keep them on dry land. You can tell they are regenerating when you see teal/blue-green floaties coming off the skelly. A few will have weapons. Take out the weapon skellies based on weapon type:
A) Sniper rifle skellies = These are your first priority. They hit from and distance and hit hard.
B) Pistol skellies = These are your 2nd priority. Their attacks become very inaccurate at a reasonable distance.
C) Blunderbuss (shotgun) skellies = Your last priority. These will need to get close to you to do damage and it's very easy to outrun them.
For most of the weapon skellies, I run them close to the dock and jump in my boat, using the side-wall for cover. I pop out and slowly kill off the weapon skellies. Once all gun-skellies are dead, I run down and hack-n-slash the rest until clear.
Shadow Skeletons - These are annoying, but there are a few tricks. If it's night, you will have to use your lantern (held high) to stun them and make them vulnerable to your attacks for a short amount of time. Try to make sure it's daylight when fighting them - that's the easy way, but not always possible. Same as the leafy skellies, hit the ones with guns from your ship to kill, then run down and kill the rest.
Golden/Metal Skellies - There is a good trick to these guys and they are definitely not the worst if you know how to handle them. They become weak in water. Good thing there is usually a shallow water pool in the center of the skelly forts! I put one of the explosive barrels in the center of that pond. Then, I lead the skellies through it (when they hit water they slow down to something like 10% of their original speed). Once they are around that, I detonate it, killing most of the skellies. IF you do not have any barrels, simply run the skellies into the pond and fire at them (guns first) from a distance, while close to an ammo box.
The waves you get will be random so I have no idea which ones you will get. But a good rule of thumb is to carry, at all times, at least 3 bananas and keep your health 3/4 full. If you die, you are wasting time that could be used killing skellies. You are against the clock at all times. The clock being other players rolling up and taking your stuff.
Your strategy should be very defensive. Only engage when you are sure you will come out on top. From the moment you get near the island, you are setting yourself up to win. Getting the boat close and at a certain angle, setting explosive barrels for use later, identifying key resources (bananas/ammo), and controlling the skellies when they spawn.
After every wave, or even in the middle of, hop on a high point on the island and scan the horizon for any ships. If you see one that is near-ish or coming your way, drop everything and head to your boat. Set yourself up for the fastest getaway you can make if things go sour. Watch them and see what the other ships does. Expect the worst and hope for the best.
Never trust anyone! I've learned that voice chat goes a long way. It's NOT WHAT they say, it's HOW they say it that will give you clues to their intentions. The younger the voice sounds, the less trust I put on them. Sad, but true for the most part. Grown-A*s people tend to understand that working as a team gets you good stuff. Teens tend to want to PvP much more and don't care much on what it costs them (very much the true pirate strategy). There are outliers, but from what I've experienced, this is mostly true.
Ok, so you killed all the waves and the final boss spawns. Kill it- usually the easiest part of all of this. Now you are done killing skellies.
Grab the key the boss drops and open the door under the main "fortification area". It looks like a door that leads to the basement. Open that door and your riches await. BUT ITS NOT OVER! Other players may still be coming. And when that skull cloud disappears, other players now know it will take you some time to get everything from the treasure room to your ship. You are now a viable target. Sooo, you have to prioritize things again.
Here is what you want to grab:
1- Is there a faction you REALLY need? Grab those items first.
2- Skull Fort Chest, Skull Fort Skull, and Gem Chest should be your priorities. Get those to your ship ASAP! On your way to your ship and the way back, check the horizon for other ships. Be paranoid. I'd rather be paranoid and leave half the treasure there than get sunk and lose it all.
3- Everything else. At this point I load up on everything else till I have it all.
Now, the final journey to sell. Are there ships in the area? If yes, go to different port. You have a lot to sell and that takes time. Find an outpost that looks vacant...then... still be paranoid! Keeping your head on a swivel will save your butt more times than not when you are going it solo.
You are the mouse, so be smart about it. Don't give anyone else the chance to get you unprepared. If they chase you, just keep running. They will loose steam. (Even better, run them by other parked ships), people are usually out for the easiest kill. Make it hard for them and they will find someone else.
At the end of it all, it's really gratifying to solo a Skull Fort. It makes you feel like a b****s. Just don't get discouraged if you get 1/2 way through and someone takes it. Soloing a skull fort really takes some luck to be alone long enough to do it. Patience is key.
Good luck out there and if you see me, I'll split the fort with ya!