It's ok to have the UTH on the plastic if you have some kind of thermostat connected to it to make sure it won't malfunction or over heat.

Just make sure you have a little gap for air flow between the bottom of the heater and the table it's on. You can put something under the corners or the sides. I used to use 1 x 2's.

Also, that tray table looks a little scary to me. If you bump that your snake tub could fall off so easy. That's just temporary. I hope.

Good luck with new tub.