How do you manage to keep your tank warm all winter?

Right now I have a 10 gallon tank with a heat pad and lamp on the hot side, no heating devices on the cool side. although the top is covered with tinfoil/duct tape. The warm side stays fine, and when I get my Herpstat next week it should be perfect all winter. I'm worried about the cooler side. Since my place gets significantly colder in the winter due to very poor insulation and crapy heat, the tank will lose alot of heat through the glass.

Although it's a small tank I have seen the cool side drop to as low as 77 while the hot side is in the high 80's (Once I get the Tstat I'll keep it above 90). This happened last night since the nights are starting to be pretty cool now.
I'm hoping when I get my tstat my cool side will stay at 80-82 since I will be able to keep the hot side more stable at night. If not do any of you use heating devices on the cool side also? or If you insulate the tank what do you use? (I've heard of using corkboard, but I'm looking for other ideas as well)