I mentioned my Cort headless guitar earlier in this thread (2 years ago). It's a full-size real guitar that's about as compact as possible.
Here's another non-traditional "guitar" that's even smaller; it's called Jamstik. It won't appeal to purists as it doesn't even have 12 frets. But I am still open to new ideas and this looks very interesting. You can use it as a MIDI controller to produce non-guitar sounds, too. And it never goes out of tune. If you're trying to conserve space in an RV this is one way to rock. You don't even need an amp. You can play it through your phone.