As anybody who is familiar with terrestrial frogs such as Pacman Frogs and Pyxie Frogs knows, you want to avoid belly heat on these burrowing frogs to keep them from being burned or cooked.
So when setting up any sort of a rack system such as those commonly used for snakes, it is best to heat the rack by running the heat tape either down or across the back of the rack system. The problem with this set up is that there is more heat loss than with the belly heat method.
After some experimentation and research building my own "rack" for my frogs, I found that the 11" 20 wat per foot flex watt works the best. I have also found that using a rack system that is enclosed on the back and sides is best, as it will hold more of the heat. For this purpose I have converted an old dresser into a shelf that holds nine 16 qt. sterilite boxes with room for three 6 qt boxes at the top or holding 25 6qt. sterilite boxes. It has three runs of 11" flex watt wired together in 24 inch runs positioned on the back peice which is connected to a dimmer switch. Temperatures are monitored by placing the thermometer probe inside a given box. Temperature readings are taken at the front, middle and back of each enclosure. The coolest part of any given enclosure (towards the front) typically run 78 F, while toward the back they reach between 82 and 84 degrees F.
On a snake rack, a thermostat should have the probe in contact with the heat tape itself, to ensure that it does not reach more than 95 degrees. The heat tape itself can safely reach up 110 deegrees F safely, which may be useful for cold weather seasons when the house may not be as warm or in an air conditioned room.
I have also found that if you solder the heat wiring onto the heat tape as opposed to using the metal clips, the heat tape warms up faster and hotter.

It's important that the sterilite containers are perforated around the top of the container to allow for proper air transfer. I do not perforate the lid, as I stack the boxes one on top of the other.

If taped in place with aluminum tape, heat tape can safely be removed and placed onto another rack system if you upgrade your set up.

I'am currently using a standard dimmer purchased from a hardware store, but plan to upgrade to purchase a programmable thermostat when I can afford to, as well as build a larger rack out of melamine. The plan is to build one that can hold three stack of three 16 qt. sterilite boxes with lids on each shelf, three shelves high, for a total of 27 boxes in all. I imagine the very same set up could hold around 75 6qt boxes if I choose to use them (some adult Horned Frogs don't move much, and prefer the security of a smaller enclosure).

I have also experiemented with the plastic three drawer storage containers that you can find cheaply, by fixing the heat tape to a board and placing spacer boards of the top and bottom of the board and then screwing this onto the back of the storage system. This system heats up well, but I have found that the open space above each drawer makes it difficult to hold heat, especially if a fan is running in the room, and it likewise does not hold humidity very well either and the heat tape dries things out rather quickly. I think these drawer systems would work better in a heated room using an oil filled radiator style space heater.