So here would be my set up:
I'd have the tub sitting with the tile on the hot side(I would need something to prop the other side up though) And under the tile/glass I'd have the heat pad.. would I need something to raise the heat pad off whatever surface I have it on? And then the thermostat probe would be on the heat pad.
Inside I'd have a digital thermometer w/ probe and the probe for that would be placed on the floor on the hotside to measure the temperature of the floor and add or subtract the temp on the thermostat as needed to make the hotside about 92*F.