How to keep tank temp up

My BP has a pretty big tank, about 3ft by 1 ft (not sure gallon wise but I think 40G?). Anyway, I have a hard time keeping the temperature up, I have a UTH under on the right side and a small UTH on the back side in the middle, I also lined 3 sides of the tank with aluminum foil. But it's dry and getting very cold here in CO so I'm not sure if there's another way to keep the temp up that I don't know of, oh and I also have a towel on top to keep the humidity up which is doing the trick. Thanks!

...Uh, what are your temps at? We can't do anything without specifics. Honestly, it sounds like you have too much heat. Are you regulating with thermostats or rheostats?

Its a glass tank right? Get some corrugated cardboard and use double sided tape to stick it on 3 sides of your tank (not the front), then tape a layer of newspaper on top. This will help keep the temps in the tank for now. I noticed a difference of about 2-3 degrees when I did this, it used to go down to 73-74 on the cooler side, after putting the cardboard, it rarely goes under 76. Hope that helps!