72f will probably be too cool for just a UTH to heat the whole cage. Remember a UTH only heats the ground, it doesn't heat air so given that in a small cage that is sealed pretty good a UTH might be enough to heat the whole thing, in a bigger cage like a T8, the UTH cant heat that whole thing. So while the floor will be 90f, the air will probably be closer to room temp and maybe a couple degrees warmer. Now if you kept the room around 78f+, you might be able to get away with it. If you are going for the AP cage, you can talk to them and have the RHP you order drop shipped to them and they will install it for you and channel a groove in the top so the RHP fits snug in there and looks clean. But if not, RHPs are really easy to install. As for which RHP, I personally use a PH3 Pro Products one which works great. I heard RB ones work pretty good too so you cant go wrong with either.