When you have a fever you don't burst into flames. *end rant*
No because your body is still thinking its cold, so even if you're 104, you're still piling on the blankets. =D
Anyway..human heating pads aren't recommended for the reasons that Joe gave. They're meant to be used occasionally, not all of the time. Plus the temp gradiation usually isn't that accurate, nor safe.
Plus, why would you put it INTO your tank? That's just asking for trouble. Not to mention a lot more cleanup when the snake poops or potential regurges on it, and it's 'cooked on'.
uke01:
UTH's are relatively inexpensive and don't get that hot, but they are meant to go under the tank, as the name implies. I usually don't ever stick mine directly on, instead I attach them to a ceramic tile that I place under the aquarium/container. It has an air buffer zone of a couple of centimeters, which keeps the bottom of the container getting too warm for the snake.
As for plastic containers..I use mainly Sterilites, and if you plan on using any of these, put them in a rack, don't waste your time with lids. Listen to experience here. I've now got 4 MIA snakes, all out of Sterilite tubs with lids. The lids only latch on the ends, and if you have a warm room, the lids are easily bendable just enough from the inside for the snakes to slither out.
I like the Sterilites for the reasons someone else described. They're all modular, most are the same height and width, so you can put them in a rack interchangeably, or if lids are used, stacked. Plus, the plastic on them is a lot more clear than the Rubbermaids tend to be, not to mention un-colored.
I must have a lot of prissy girls in my town, all of the Rubbermaid stuff I can find is either opaque or pink/blue with sparklies in it.
I tend to get larger tubs than most people keep their adults in. I'm not sure of the model # anymore, but they're 3ft long by 18" wide. Some are nearly 20" tall, while others are around 5" tall. But the adults seem to be the most comfortable in them with the room.
I have some Iris shoeboxes and love them. Very clear plastic, sturdy. And I found them at Costco for $14 for 12 boxes, which doesn't seem too bad.
But all in all, if you're not going to utilize a rack, don't get plastic boxes. They look extremely tacky, have been totally unsecure for me..and for the amount I've spent on replacements I could have bought nice cages instead.