Hi 69 Avion,
How difficult a job is it to put new flooring in an Airstream? Can you unfasten the top shell, elevate it, and put in new plywood? I would imagine that there are some plumbing and wiring concerns along the way.
I have my eye on a 50's single axle Airstream that will need a total rebuild. It's a cute little rig, good for a couple weekending and will probably pull easy.
Maybe sticking a whole new platform with running gear ala' your C-11 would be a better solution. I can only imagine the state of the axle after sitting for 20 years, although I did rescue a boat trailer that was sunk into a swamp a couple of years ago.