First answer: Rubbermaid isn't making new boxes at the moment. If you want to make a rack, go out and buy the boxes you like and build the rack around those. Get extra. Boxes first, rack second.
Second answer:
Boxes are made of polypropylene for the most part, and this stuff melts easily. You need a thermostat. Period. This is how you keep the animals from cooking and boxes from melting. Contact Big Apple Herp , Helix, GCS, etc. Controllers are on the classifieds here on kingsnake.com all the time, so there is no excuse for not getting one and overheating your animals.
Third answer:
You can get those ready-made melamine shelves to make a rack. Then you don't need a table saw. The catch is you are at the mercy of the shelf size offered. Use Flexwatt mylar-coated heater for easiest method. This is available at The Bean Farm, Big Apple, LLL, etc etc.
What about buying racks online? No tools required.