Morgan, They have constructed cars with steel body panals over an Ash framework by hand for a looooooong time. They still have a steel chassis frame though. (MGTs were the same way) They all have rot problems, and the wood is very labor intense to replace.
Jaguar, Austin Healey, Aston Martin, and Land Rover (to name a very few) all have had full, and/or partial aluminium bodys. The problem there is that aluminium can corrode just as bad as steel rots. Espically where the steel and aluminium are attached togeather.
Most cars are really 100% repairable, it just depends on how much time and money you want to throw at it. But I think what you mean is somthing that can be taken apart with a wrench. In that case I would look for a classic with a body-over-frame design. In the LBC world this would include; any of the MGs before the B (MGTs, MGA). Triumph TR2-6s, Triumph Spitfire, Morgan, Austin Healey (except sprite) Sunbeam, and several others.
But for now I hope you enjoy your midget as long as you can. I kept my TR4A on the road WAY past it's need for a complete overhaul. And thouroughly enjoyed every stinky, rattly mile!
Good luck Guv'na