I like RHP's I would suggest giving one a try. They are efficient to use, and if the animal is always perching, you can set up a perch at a safe, temp-measured distance underneath.
That said, I am experimenting with a planted tank that has a UTH inside the tank. It is sandwiched between some thick styrofoam and a piece of slate. Carve out the foam to fit the bulky areas so it all lays perfectly flat. Use plenty of silicone to seal around, and set in elevated above the surrounding substrate. Since that t-stat probe is now permanently affixed to this UTH, I ordered an extra probe in case the project doesn't work out. (VE t-stat probes are removable, and I would guess the Herpstat models are too, but don't know for sure. My Hydrofarms are all one piece.)
DYODD on this, folks. This is *off label* use.