If you use the R-Tech foam, DO NOT cut it with a hot wire! The fumes are nasty, and probably not good for your health! I've found that a serrated knife works extremely well, with very little mess. One nice thing about the R-Tech is that you can use hot melt on it without putting holes in the foam.
I'm not sure about this, but one potential issue could be the aluminum foil backing, particularly if you run TMCC or Legacy. I have not worked with it enough to know if the foil needs to be connected to earth ground or not.
Chris
LVHR