You state that you have tools and carpentry skills. It would be so much easier to just build some enclosures that you can stack. Your dimensions mentioned are 1" shy of the ones I just built and realistically it could have been completed in a solid weekend. I built 2 for aprox. $300 ea. Complete with RHP, thermostat, thermometers, hygrometers, substrate... All but hides and clutter.They are stacked with an 1.5" air gap (2 pieces of scrap from build, now I know it works I can make something nicer looking) between that I learned through trial and error was needed since I mounted the RHP on the ceiling of the lower one and the heat bleed through to overheat the floor of the top one. My cost could have been a bit lower if I went with thinner and less expensive plywood like you mentioned. It was only $53 in wood per cage using 3/4" pre-sanded hardwood ply. 1 package of Pond Shield covered the inside of both cages and now they are nice and sealed against the humidity.