Hey Joe,

Wow did the Big Ten take a beating this year (I'm originally from Midland and CMU)! Anyway, if your just cutting a hole (let's say 2" sq.) to gain access behind the firewall, you can cut a trim piece with about 1/4"-3/8" overlap and cover no problem. Just tack/seal on side, check the fit (you can always pull and cut a larger trim piece) and tack the remaining sides. You don't need a heat gun, just run the iron over the 'hole' and it will tighten up. Make sure you don't stay in place to long, keep moving, heating, and checking. Let cool to tighten and reapply heat as needed.