T8 heating questions

An 80 watt RHP will be more than enough for a T8. You are talking a cage that is only 11.5" tall. I use a 65 watt Pro Products RHP in my Pro Line cage in a 75F room and it is only on maybe half the time in winter. You will be plenty fine. Also I don't use UTHs as I don't like them so if you are using that, you will definitely we fine.

I use a PVC cage 36x24-12 inches high. 40 watt RHP on one side controlled by a thermostat. My room temps are the same as yours. I never use heat tape. I get the correct temps and humidity easily. My BP has never had a bad shed. When he starts to go into a shed....I will toss some wet moss in there....jumps the humidity up from 55 to 65 ish. I have a large heavy water bowl in there also. You can move it closer to the RHP are farther away to adjust a little bit for humidity. I put a temp probe inside of a short paper towel roll and secure it from the top with a zip tie. It hangs in the tube a little more than an inch from the cage floor. the ambient temp near the floor of the cage is what needs to be in the correct range. You do not want the thermometer probe in the sight of the RHP...you want it blocked. This way the RHP isn't heating the probe surface and you are actually measuring the air temp. I'll check the far cool side, the middle and the warm side.