Not just the top......Epoxy the entire tank befoe the install.
Here's how I do it.
Wash the tank with wax & grease remover using the 2 rag method.....Standard stuff when painting boats or cars.
Then tape the areas you don't want epoxy on. Like fuel nipples.....flange for fuel sender.
Now with 80gt on a DA samder....Sand the tank. This will give a good tooth for the epoxy to hook to.
Blow it off.
Wash again with wax & grease remover using the 2 rag method.
Then apply 2 coats....rolled On of Coal Tar epoxy
You have now protected the tank from the elements.
The foam to use......
Not that Damn expandable foam in the box store for houses.
Yes I've seen people do it.
You want 4lb density foam.
http://www.uscomposites.com/foam.html
Be SURE the tank is fastened in BEFORE you pour any foam. If you can't fasten it in.......Then with a 4X4 across the deck locked in and a floor jack on top of the tank,,,,applying pressure to hold the tank in place.
Failing to do that......You will have a mess and possible that you will be cutting the tank back out.
Don't let that tank Move!
Foam is 2 part mix and pour no more than 16oz at a time.
But before you stat that.......Use visqueen plastic sheeting all over the deck.....Tape it down.....You don't want foam on the deck.....Mix the foam In the boat on the deck.....You don't have time to climb in and out.
Spillage will happen with the pouring...mixing and pouring of this stuff.
Yep I've done a few tanks.
A 29 SeaVee I did had 3 tanks in it.
I use Coal Tar Epoxy. A 1gal Kit will do your tank.....A gal kit = 2gal.
Then trim the foam flush with the top of the tank and fiberglass bridge from the coffin over onto the tank.....Be sure there is a limber level with the top of the tank, if any water or moisture settles on top of the tank that limber will allow that water to go to the bilge......and not just sit on top of the tank.
