The way to set up a backup thermostat is to plug your heat tape into a proportional thermostat like the Herpstat from spyder robotics. The probe from that thermostat will sit directly on the heat tape. You will then plug the proportional thermostat into the output of a on/off style thermostat such as a Ranco. The probe from the on/off style thermostat will be placed on the heat tape as well.
Now you set the proportional thermostat to your desired temperature. The on/off style thermostat will be set at the maximum temperature you want your heat tape to get ever.
So this is how it all works. The proportional thermostat regulates the heat tape unless something goes wrong with the thermostat. If something does go wrong the on/off style thermostat will kill the power going to the proportional thermostat until the heat tape cools down to safe temperatures.
Also to comment on the AP racks: because they are made from 1/2 inch thick PVC they hold heat and humidity in very well. They are great, I defiantly would recomend them.
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