I already had some small heat pads that I had to cut just a bit (just a little off one of the sides) to fit, but they slid right in. The slot is 4 inches wide and very slim. That's for the BP cages though. I am not sure about the larger cages. I would assume the slot is bigger.
Heat tape would most likely be better, I am sure, if you could get it.
I ordered the stuff on the 6th of Sept, but he makes them when you order them so it takes a bit, which is fine. I got them on the 21st.
If you call him up, he'll answer any questions you have. He picked up the phone right away when I called.
If you're in Florida, he's going to be at the Sarasota Repticon this weekend. He might bring some extra stuff so you can check it out yourself.