Been running POR15 tank sealer for almost 10 years now. While I have not used it a lot I can say the one on my 37 looks dang good. Sometime ago there was a good thread on this and lots of folks talked about it "cracking" but investigation showed it is NOT prone to cracking. You can see straight down into my tank and it has held up very very well.
However, I will agree with Scott. After $75 for the vat job and another 50-60 for the kit ect, it makes you wonder if the money you saved is really worth it when, depending on your tank, one could be purchased with not much more money. Buy a new one and give the old one to a guy who has none!
.....and your luck you found a shop that would vat it!!