I wouldn't go commodities, requires gold investment and puts you in a situation where you need to be somewhere to get the return, randomness gets in the way
I'd go merchant shipwreck voyages and small island dig captains which have a decent enough chance of mega kegs
take out skelly sloops for easy loot and megs, megs have a high chance of merchant items and often will have ancient bone dust
not too hard to work merchant into gold rush hours as well for the daily bonuses
sell gems to the merchant if you aren't using the sovereign
always go emissary when chasing gold, don't fear the reaper
just adapt to them as needed
You want to keep moving and cut down on transport time
what I listed above allows that, never be a sitting duck for a long amount of time, it's not worth it
Vaults are eh for a solo, too much island time, too much transport time, too much sitting duck time, there are more efficient ways.
Consistency is efficiency