We are renovating our bathroom and are about to install a new porcelain on steel bathtub. We were thinking about spraying around the sides of the tub with expanding foam insulation for support and heat retention. My concern is how much the foam expands and could that distort and crack the tub. It seems there would be plenty of ways for the foam to expand in other directions. ALSO we were thinking about doing this before we install the tub so we can trim off excess and minimize pressure problems. Any thoughts or experience with this?