I foamed in my aluminum day tank with 2-part more than 30 years ago, and it held up beautifully. The force of expansion was not an issue for me; I was prepared to put water in the tank as the foam expanded in order to keep it in place but that was not needed. As for corrosion
, it was not a problem on the exposed top of the tank or the sides and bottom against the foam - the tank location was dry. If salt water
were to have been in the area I'm sure it would have soaked into the foam and corroded the tank. I did glass over the top edge of the tank and the top of the foam, which provided a good barrier to liquids. That said, I had a stainless steel
kerosene tank located on the shelf above the day tank and it did corrode internally and slowly leak kerosene, which soaked the wooden bulkhead and much of the foam around the day tank. Now that was a stinky mess. Ultimately, the aluminum tank was corroding on the inside at the very bottom from water and dead algae - the outside never became a problem.
Most poly tanks in the US are not sold these days for diesel
, I think because they do not meet the low permeability standards. IIUC the rotomolded fuel
tanks have a low-perm coating on the inside; the welded poly tanks don't. Also, there are thermal expansion issues with using metal fittings with tapered threads into poly tanks, so appropriate plastic fittings should be used. The European metal fittings with (somewhat loose) straight threads and gasket
seems a lot better. Reluctantly I will be having another aluminum tank made.