The only thing I can help you with is to tell you to be sure you have epoxy and NOT polyester Resin. Polyester will eat thru just about all foams.
A quick story. I saw a boat that had been holed and sunk. It sat under water at the dock for an entire winter. It was raised in the spring and they filled all the holes with the spray foam from home depot and then moved the boat. The guy that was working on it said they used spray foam all the time when raising boats.
So thats my story on foam.