A "wire" like a #10 copper wire for instance, will not work very well to make a good RF ground plane. You would need to use something like a wide copper braid strap. Even then, the antenna really needs a ground plane directly under it to work very well. What RV are we talking about? If you have metal framing: metal studs, metal roof trusses, etc. then you may do okay. If you have a wood framed RV then it won't work well.
Years ago Radio Shack used to cell a CB antenna that was advertised for marine use and didn't need a ground plane. I don't remember the specifics of how it was constructed. That's what I would do, look for an antenna that doesn't require a ground plane.
Technically, your RV does have a ground plane in the frame, engine, and any other metal but it's generally too far removed from where an antenna would go.
