This is why you don’t foam in an aluminum tank.

http://i21.photobucket.com/albums/b2...enname/9_2.jpg

This is from a Donzi I did last year. Not a boat you want a failed fuel tank install in.
This was a mid-west boat (fresh water). Tank was less than 10 years old. The whole thing was coated in coal tar. Then put in place and foamed in. The issue was the front bow eye leaked (another impossible thing to fix in a Donzi without taking the top off). Water rolled down the drain and over the floatation foam and on top of the tank. Between it and condensation the coal tar was pulled off the tank by the foam and then the tank was turned into swiss cheese because the tank could not breathe (air circulate around it) or expand and contract.

http://i21.photobucket.com/albums/b2...enname/3_6.jpg

The new install is done like my 1972 Allmand SuperNova was done (43 years later and the tank is as good as the day it was made, I had it out 2 years ago just for inspection). Cut up rubber strips (I used a couple found tractor trailer mud flaps) for it to sit on and for the sides between it and the stringers so there is an air space and it’s not sitting on fiberglass anywhere. Liquid nail the strips in place and a couple more dabs on top of the rubber. Squeeze tank in place and then block it in with some teak blocks and stainless steel screws. The tank is there to stay and the way it’s installed even though this boat is on its 3rd tank it should be its last for a least a few decades.

Same way my velocity tank was installed from the factory. Ill be putting it back in the same way.

ok,,next time your outside find a brick...get a piece of aluminum foil,,set brick on the foil.lift up the foil by the sides.now go up and down real fast...let me know how long the foil lasts..