I use flexwatt for all my AP cages. Ultratherm is basically the same thing. Just Ultratherm only comes in precut sizes where as flexwatt can be cut to pretty much any length. And just so you know, unless you are an electrician, it is illegal to wire up heat tape. I actually didnt know that until i talked to the owner of Bean Farm and his wife since i live close to them and go over there to get a lot of my stuff.

And to answer your question on which ultratherm to get, you want whichever one is about 1/4 to 1/3 the length of the cage and the full depth of the cage so something along the lines of 12-15 inches wide and 20-24 inches long. Like i said, i personally just went with APs flexwatt as i prefer to just get everything in 1 shot and i dont mind spending the little extra with them as they are a smaller family company that does an awesome job. Just be aware, AP LED lights dont last long lol. One of my T25s lights are dimming on me already. Time to call Ali and get a new set shipped to me. Not going to be fun pulling Caesars T25 off the stack to get to Vicky's top