It's not that simple, every rack is different, and every room is kept at different temperatures. This means that you will have to figure out what to set your thermostat based on what your temp gun or probed thermometer says. You need to set your thermostat to whatever temperature results in a 88-92 degree hot spot inside the tubs.
Start out setting your thermostat to 92 after an hour take a temperature measurement inside the tubs and see what temperature they are. Then adjust your thermostat accordingly. Repeat this process until your tubs are reading between 88-92 F. During this process there shouldn't be any snakes in the rack.