Our 3 step cycle tank kit will work great for you. Choose the 5 or 12 gallon depending on your size tank.
Step #1 is cleaning with AquaKlean to thoroughly remove gum, varnish & fuel residue.
Step #2 is a quick coating with RustBlast to leave a zinc phosphate coating for good tank sealer adhesion.
Step #3 is Gold Standard Tank Sealer. Fiberglass is very porous & our tank sealer will seep into and interlock with it to cure into a permanent, nonporous, fuel & additive impervious coating.
Our complete instructions are posted here:
http://www.kbs-coatings.com/Gold-Standard-Tank-Sealer-Information-Instructions_ep_39-1.html