Tank coffin question
 

Short version: How important is it to have a fully watertight enclosed fuel tank coffin?

Long version: I'm planning on installing my tank using a modified pascoes method. I've already sprayed 3 heavy coats of epoxy paint. I've glassed in support slats spanning from stringer to stringer about 4" up from the bottom of the bilge. I've glued FRP strips to the underside of the tank which I'll bond to the support slats with thickened epoxy when the tanks gets dropped in.

My question is do I need to install watertight bulkheads fore and aft of the tank, or is it okay for the tank to live in the bilge compartment? Though the bilge pumps should ensure that the tank will never sit in water, the tank will almost certainly get wet every now and then, but with the marine epoxy coating and the pascoe install, is this really a big deal? Obviously I'd like to get 20+ years out of this tank, but I'm wondering if the bulkheads are necessary. I imagine even the bulkheads would need a drain to allow any water intrusion to escape, so even then it wouldn't be watertight

IMHO it's not a good idea. Water will find a way in and you don't want to trap water around your tank. If you seal the hatch above the tank you won't be able to easily check.

So long as the bilge vents well.