rack, rack...

[Caveman]

First of all, I want to say hallo to all of you, snakes maniacs! Recently, I've been considering building a small rack for three snakes: boa constrictor, brazilian rainbow boa, and boa constrictor again. I'm just fed up with using my old, typical wooden cages- I've never been too fond of so called vivariums. So, my question is: how am I to heat such a rack? With heat pads? Where to place them- on the back? Or maybe under the rubber maids? All suggestions will be wellcomed!