Alright, so I don't currently have an UTH set up (using a heat lamp), but I've decided I should set it up sooner than later because the light's not quite working out (Warm side temps perfect, warm hide too cold; warm hide temps perfect, warm side too hot). I already know not to use the UTH without a thermostat, and I've got a Herpstat 1 Basic in the mail that should be here by next Tuesday, and should y'all's advice work out then I have a rheostat to hook the UTH up to until the Herpstat arrives. The UTH I have is a ZooMed ReptiTherm that's the right size for my tank (20 long).

Alright so questions:
1. The instructions for the ReptiTherm mention side- or back-mounting if bottom-mounting isn't possible (more on that later). Would you guys advise that for a BP's tank?
2. Where do I put the probe for the thermostat? The guide on here says between the UTH and the tank, but the UTH pictured has a space between the heating elements for the probe; the ReptiTherm doesn't. One of the guys at the Reptarium (reptile-only pet store) said the probe should go in the tank, where the snake will be feeling the heat. I've seen posts on here, however, that doing that opens up the possibility of the probe getting wet, the t-stat thinking the tank's too cool, and heating the UTH to the point of potential burns. Which should I do?
3. Alright getting into why bottom-mounting might not be possible. I currently have Maggie's tank sitting on a wood dresser, one that has some sentimentality for my mom (whom I live with). It's a dark wood dresser with some kind of finish on it. She's worried about the UTH discoloring/scorching the dresser and/or starting a fire. I'm trying to assure her that the rubber feet included with the UTH will elevate it enough, and that we could lay down a piece of wood or something between the tank and the dresser or get taller feet. Anyone had any problems with scorching/discoloration? Are my suggestions of a big enough board beneath it/taller feet good ones? How likely is it that a t-stat regulated UTH would cause a fire?

I think that's all I have for now, I'll ask more as they come up. Thanks in advance!