Re: Fiberglass tank...
You know, come to think of it, before I went in the hospital (just spent 4 months with a failing liver before they found me one) I bought a video from some guy who shows how to make custom fiberglass tanks.
He uses that Caswell sealer. If you are tempted to find and buy the video, do not waste your money. Confusing, poorly made, hard to follow, what a waste of cash that was.