It's not a good idea to have any electrical devices INSIDE the tank. Keep the heat pad underneath and outside of the tank. I think the biggest mistake most beginners make is keeping the tank too hot. I try to keep the warm side of my tubs between 86-90 and try to make sure it never goes over 95. I don't generally concern myself with the cool end, but then again my snakes are in a room which is generally between 75-80, but even in the winter when it gets colder in there I don't get concerned. You're never going to achieve perfect temps all the time in any kind of cage, snakes kept too cool might be uncomfortable, but snakes kept too hot can die. I personally think it's best to err on the side of caution. As long as they have temps close to the 90 degree range sometime during the day they should be fine.

Also, don't guess at the temps. Those stick on dial thermometers are next to worthless and those color changing strips that change colors like a mood ring are even worse. I think anyone who has a snake or even a reptile of any kind should have a temp gun like one of these - http://www.reptilebasics.com/pe-2 I have several laying around my snake room and use them every day. frankly I think they're just as important as the heating devices themselves.