Cleaning and preparation of the tank is paramount. Very time consuming. I would look into the latest type sealant. Military and airlines are using the EFC -100 ( they have products for both jet and av gas type fuel.
It can be sprayed or brushed on and when it drys, it is like a fuel bladder. Flexible ,long lasting and is not deadly like poly-sulfide to your lungs. Even with a respirator getting the smallest amount of fume creates havoc with that poly-sulfide stuff.
It has good long workable time--------------look into it.
