Thanks for the very interesting info on Guitars and RV's.
Being an alien (as the border people say), we have to leave our trailer to the elements in the summer and winter (for some reason we prefer the Spring and Fall for our travel in the States). When we say that we leave our instruments in the trailer we get sharp intakes of breath, like a plumber about to give a quote, and advice that the glue used on guitars will break down above 120 degrees.
However we have had no problems so far. We place each instrument in its case, in a vacuum bag (no vacuum, just most of the air removed). Each time I have the internal debate about detuning, and have come to the conclusion that it sits at home for months without any problem, so the first couple of times I backed them off, but now I have left them fully tuned. So far we have had no problems (summer humidity in Orlando and arctic cold in Dallas).
The idea of the folding guitar gives the same feeling as scraping nails on a blackboard, but the you tube video seems to show it working.
As for portable instruments I rather like the idea of an inflatable double bass.