I have used the Caswell epoxy system 5 times now. The last tank I did sat for 16 years full of gas (ugly), the key is do a good job cleaning the tank out, after draining I put in a few quarts of good
solvent and let it sit overnight, then a long cleaning with a pressure washer and strong detergent, flush it out till only clear water is coming out. Blow dry (oil free) compressed air through it
overnight at about 5 PSI. Coat the tank per instructions, I have had excellent results, would never consider a single component system again (had a bad experience once). Its a bit expensive,
like $80 on EBAY, but well worth it.