Plywood will not help. Insulation will not help either, within reason. Understand that insulation only slows the radiation of heat or cold. It does not stop it. So being in a basement, the earth wins.
If I were to attempt that and with my experience, I would heat the floor. I think I would run pipes, mostly copper and circulate hot water thru them.
The sell these inline hot water recirculating pumps. They are so fancy dancy folks can have instant hot water. You can get a small water heater and work from there.
I would then build the cage over that. This way, you can control the mass temp of the substrate. In my opinion, you only have to create a medium temp, say mid seventies to low eighies.
Again in my opinion, mass temps are far more important then air temps. Monitors/most reptiles, understand mass or surface temps, and could careless about air temps. Cheers