Just something to think about... Particle board, MDF, and most plywoods contain formaldehyde, these product also contain many poisonous glues and fillers that can be hazardous to your tortoise. The warmer the cage gets, the more formaldeyde is released into the environment. You can actually smell it if the wood is warm, or when you cut the material. The chemicals found in products like these don't evaporate out. They are bonded at the time of pressing.
I would suggest using oak, maple, or poplar... Hardwood. Better yet look into a plastic container.
I have a young Burmese Black Mt. tortoise which I constructed an "inside" cage for. I went to Lowes and bought a plastic mixing pan.. $10
, and built a poplar box around it. I also insulated it with styrofoam. The pan measures roughly 4ft X 2ft X 10inches deep. This setup is extremely easy to clean and disinfect. I don't need to worry about mold or fungus growing into the wood, nor spills destroying the floor. Clean, easy & safe!
PB and MDF also expand and hold moisture which can cause fluctuations in humidity levels.
I think what you have will work just fine, I just wanted to point out some things that many people do not know about man made woods, laminates, and particle boards... MDF etc...
-Kory