No I have never foiled a tank i turned it. Um here is what I have done to a tank.
http://ball-pythons.net/forums/showt...arium-Solution
I have used this material,
http://www.kent.ca/kbs/en/product.js...2&catalogId=45
I glued a image to the snake side and the one side visible to me I just used black paper. then just taped it to the outside. if you get thick stuff it is hard to cut.
At the moment my cool side temps are at 78.5, 81.2, 80.1 and 79.3. each tailored to the occupants, I have 3 cool one hot at the moment. you sound like your temps are fine.
Alex