I had one that matches your requirements. 1986 Escaper, see my avatar. It had a full time rear bed (large twin) and of course the overhead bunk. Side wet bath. Downside was the eating area, a table on poles. Ground clearance was just ok, drove on a lot of BLM and Forrest Dept. roads, NO jeep roads.
If you don't mind making up a bed each night then a Rear Dinette model is a bit more common. Actually they mostly all have an overhead bunk and a convertible Dinette.
+ & - are mfg's marks to show slight variations in advertised spring rates, usable for fine tuning.
NORMALLY + would go on the heavy side as its a bit stiffer. You have weighed your Toy front to back and side to side,,, right🤣
New product. It is a replacement for luan wood if your having to reroof/reskin your RV. You still need the frp/whatever outer skin.
https://azdelonboard.com/
When you find the reservoir, read the owners manual carefully. Toyota often specifies special fluids other than "power steering" fluid. The wrong flavor is bad juju.
A 225/50/12.5 tire turns 944 revs per mile, a 185/14 LT turns 819 revs per mile so your going to be working your, no power, engine harder. Steel rims with correct offset and bolt pattern are problematic.
Do you have dual rear tires? (4 tires)
The four bolt hubs are going to be the main sticking point.
Most of us have Hilux based campers, the Townace is a JDM model
"Normal" RV wiring is white is - or ground and black is +. A volt/ohm meter will be the easiest answer. Measure the resistance of the white wires to the frame, it should be almost 0 ohms.
A 4x8 equivalent weighs 29lb and would cost $99 if you bought 8' lengths
https://www.farmtek.com/prod/duracladr-interlocking-multiwall-panel-16-w-x-96-l.html
I don't know how useful this would be in redoing a Sunrader, but redoing a gutted stick built it just might be the right stuff.
https://www.palram.com/us/product/duraclad/
It's around $32 for a 16"x 8ft or $50 for 16" x 12ft