I think a IR temp gun is by far the best way to monitor your surface temps. Using a rhp it is really important to know what the actual surface temp is.

For my ambient temps I use the Accurite units and find they are good at what they do. I have four units and beside the one I dropped and broke they all agree with each other on the temp of my identical cages in my snake room.

I would not mount your probe to the cage ceiling. That will not be reached by the heat and the surface temp will get way to hot. I Like to mount mine to the edge of the rhp. I glee the probe into a cable strap and then glue it to the edge of the rhp so the probe is sticking out directly under the rhp but not touching it.