I have a T8 setup with 2 40w RHP's (because I used the divider in the T8). I have only used Reptile Basics' RHP, but I will answer your questions as well...
Do you have any other heat sources in the enclosure? Yes, I also have 12" heat tape from RB on the bottom, but I have my thermostat for it set low and it only runs if the house gets very cold.
What are the temps in your room? Winter - 65F-72F Summer - 68F-78F
What are your warm side/cool side temps? Warm side: surface=90F, Ambient= upper 80's. Cool side: Surface 82F, Ambient=77-80F
What substrate do you use? kraft indented paper
Do you have the RHP centered or is it biased to a certain side? Off-center to favor the warm side. They create enough heat that doing this assists in giving you a warm side/cool side gradient.
Any issues mounting? Nope. You can pre-drill if you want, or if using a coarse thread, like a drywall screw, no need to pre-drill. If you use the enclosed screws, you're fine. If you use your own screws, just make sure they are not long enough to go all the way through the mounting surface.