Ditto what Vaughn said.
I don't like human heating pads because .... well they were made for people, not cages. They were not designed to be run 24 hours a day 7 days a week. Also, they are very prone to developing "hot spots" and cooking snakes.
I also really don't like putting electronics inside of a cage. Accidents happen ... water bowls spill, snakes get tangled in cords, etc .... It would be different if you were there to keep an eye on things 24 hours a day, but ya gotta sleep sometime!
Just my $.02
-adam