i've never had trouble with humidity while using a heat lamp, so here's how mine was set-up before i moved over to UTH's.

make sure the heat lamp is on the OPPOSITE side of the water dish. also, what size water dish are you using? i have one that is about 10 inches wide for my pastel BP, and she always has nice sheds. so if your snakes water dish is on the small side, even just providing a larger one can do a lot for the humidity.

but as others have said, the humid hide is probably the best idea, however my BP wouldn't use hers.