It is not double stick. personally for the cost of the pad I'd just stick it and replace it when I needed a new tub. Taping the bottom is one way I have a few like this I use a temps for rescues. The UTH are not expensive and sized differently chances are if you change tubs for a larger one the small uth from the last one is going to be too small. I keep the tub with uth attached and just use it again. if I need.

thermostats are needed a rheostat at the least but they often require adjustment as the room temps change so they can be a lot of work and worry if your room does not hold a steady temp.