Okay, I'll bite. Can you tell me more about this tank?
And yes, stainless doesn't like to be covered as such a condition can lead to crevice
corrosion. It will probably find faults in the welds first (from welding inclusions, imperfections, or... well.. crevices). So not sure why you want to
paint or coat it. In either event if you're considering coating it you will have to
lift it to access the underside, so I gather it can move at least a little.
Maybe you could be better served by building a
fiberglass box or container to place it in, or
lift it up on a small bulwark to separate it from the
bilge, so the
bilge can move freely and around without immersing the tank?