Not sure I understand. You have Thermolam 971 and don't know how it will hold up? I looked it up and it is fusible fleece. Fleece should hold up just fine; it is simply a napped polyester knit. Although it is more often used as batting, I don't see why it wouldn't work for a snowman. Did find these reviews of it:
http://www.overstock.com/Crafts-Sewi...r-reviews.html