Heat tape

When it comes to rack systems, could somebody please explain to me the different pros and cons with the heat tape on the bottom as compared to it being across the back.
Thanks in advance.

In my opinion the back heat would be better for a room the is very stable temp wise, say around 75 or maby a little higher. The belly heat would be able to heat alittle better in a colder room. I perfer belly heat myself...

I agree with Matt.
I have a couple of racks in use currently that use the heat from the back method. In my heated herp room this method works fine, but I have no adjustment to the tape. It runs wide open to bring the cage to the appropriate temperature due to excess heat dissapation from the tape.
I have measured the temperature in my hatchling rack with a Raytec and got the following results:
Base of the back wall - 92°F
Rear floor 2-3 inches from back wall - 84-85°F
Front floor - 74-76°F

In more normal temperatures of a room in the house, this method of heating would be inadequate.
When I build racks in the future, I plan to return to heating the boxes from underneath. A thermostat will be required, but I will regain the ability to adjust the heat tape to the temperature I want rather than having it run wide open to bring the temperature high enough.