Just be careful that you don't use that stuff in a confined, or closed area of the boat. It needs room to expand.

My old clark Craft catalog shows the proper aplication of expanding foams in sealed areas: make the area in the hull without a top. Fill the area with foam, which will probably overflow. After the foam has cured, level it off. Then fit the deck on top. Otherwise, the force of expansion can cause the hull or deck to bulge, and possibly loosen or break a seam.

if you use the less expensive sheets of build foam you can shape them to fit the curvature of the hull eaasily. Use spots of rubber cement to tack down a sheet or two of coarse sandpaper to the area you want to fit. With slight pressure on the sheet of foam (lean on it a bit) slide the block of foam back and forth until the sandpaper removes the extraneous material. Lift up the sandpaper and rub off the rubber cement.

It is a good idea to seal the foam inside a layer of fiberglass cloth and epoxy resin, as this strengthens the foam and keeps it from flaking into little pieces. Be sure the resin layer is complete so no water or water vapor gets into the foam.

PGJ