So, I just completed a skull fort on my solo sloop. I was even able to hand in all the loot before anybody sunk me.
I fought off probably 6 galleons and 5 sloops and was sunk twice in the process so I did have to return. The waves of enemies were sometimes easy sometimes a challenge depending on enemy type and whether they had guns or not. Overall it was a rewarding experience.
There is one thing I want to emphasise though. It was utterly EXHAUSTING. It took about 2 hours including all the PvP and though it's not really the most efficient thing to do, there is a strong sense of achievement. That's rewarding. But god was it exhausting. I don't think I'll ever be doing that again!