so here is my plan. i have thought about this, and considered every option.
i will use the 55 gal, splitting it in 2 down the center, using lexan instead of plexiglass. i will use a large undertank heat pad, exotera, or another name brand. the heat will be in the center under the divider. that wold make a nice heat spot in the center for each snake to crawl onto. i am building a second floor near the center of the cage (or the dividers, that way the snakes have a few more hides, and a higher level closer to the lights. i am going to put 2 lights on the hot side. one for each snake. they will be simple 50w, but i am going to make the seond level in the cage high enough that they would be within the heat of the lights. the second floor will be made of lexan and secured with silicone. i got romoanesque collums to support the second floor (made for a fish aquarium). to keep the humidity up i am using lexan over the open parts of top of the cage, with air holes, and making the DIY hummidifier, so it keeps the ambient humidity at a nice level. with the combination of that and overturned plant potters covered in dirt (with wet moss inside), i shuold be okay on humidity. i dont think i will put insulation near the cages.. i would be worried about pieces of fiberglass falling into the snakes cages. i am sure there is a way i could fic it so that there would be none falling in. would the insulation boards across the back, and sides help keep heat in that much?
thanks for the advice... soon i hope to get a digital camera (yay x-mas), and i will take step byu step pics of this set up, and post them.