I use these intellitemp reptile heat mats to heat my burm cages, they're waterproof and easy to regulate with a thermostat and have held up really well over the years. They're about the only heat mat that I feel safe putting inside a cage.
http://www.bigappleherp.com/core/med...7850ec0b742e7c
Also, I really don't like the use of hardware cloth on a snake cage. It's too easy for them to rub their noses raw.