Custom Snake Cage Advice?

Up until this point I've been using large aquariums and infrared lights for my BPs, but it's not a great arrangement because I'm ending up heating up an entire corner of the house, and all the humidity is escape through the screen tops. So....

My dad and I are in the process of designing some snake enclosures and I'd love some advice. I'd like to have three stackable cages, each 48in x 18 x 18. They will have glass on the front and the rest will be wood. He would like to use 5/8 in plywood, would this work? He mentioned that plywood is often made of pine, and I know pine is bad for snakes. Would it still be a problem if the cage is stained and coated in polyurethane?

Also, I won't be using lights to heat (thank goodness) since the cages are stackable. I was thinking of using Big Apple Flexible Heat Rope or some other type of heating cable on ~ 40-50% of the inside to provide a temperature gradient with a thermostat to prevent against overheating. Does anybody have any experience with a set up like this? Or any advice as to alternate heat sources? Neither of us are master electricians, so I don't want to do anything overly elaborate.

Ideally, these cages below are similar to what we'd like mine to look like (I just grabbed these images off of google)

http://img.photobucket.com/albums/v1...3/IMG_0485.jpg

http://www.arbreptiles.com/cages/4x2.jpg

Sounds like you have the right idea. if youre using plywood, make sure whatever you coat it with is completely nonporous, because you're right, pine is poisonous to most snakes, and the adhesive used for most plywoods are also not very good for... well, anyone, really.