:D That's pretty much what I meant with glass - it is VERY slow to heat up, and usually the heat from the pad underneath isn't enough to heat the whole thing, thus the sides and back stay cool and mess up ambient temps.
Anyway, yes that rigid foam, or blue house foam as they call it at some stores, is exactly what I use on my tanks. I use foil tape to put it on.
http://i184.photobucket.com/albums/x...insulation.jpg