I have been using a product called "Peel and Seal" from Lowes. It is sold as a roof repair item, but it's basiclly the same stuff as Fatmat and Dynomat and its a fraction of the price. It has a 40 mil asphault base covered with an aluminum foil top. It is adhesive backed so you just peel it off and stick it where you want it. $10/roll.