There are some 2 part foam that does not re-expand. Futher testing on what you want to use may save some headaches later. Seems you have already "test" the 2 part foam. Now take what you have and place it in the sun and let it get warm. Better yet, put that in an atic (if you have one) and let it sit a day or two. The outcome may surprise you. I had a 6' deep v sitting in the atic for a summer. Went to move it one day and the front was split wide open. I know for a fact that 2 part foam was sitting as it was for over 10 years before I got the boat. Stupid me put the boat were it got very hot during the summer.