With a motor home, it would depend on the composition of the glass in the motorhome. However in the recent past, I have used only on-glass antennas for VHF/UHF mobile work. They work well (unless the glass has some metallic content), are easy to mount, and when removed (and the glue cleaned up), leave no scars.
For HF, I would definitely mount it on the bumper making sure to be as far away from vertical aluminum framing as possible. Perhaps mount it on a metal plate platform you build to mount on bumper.
Ken W7TS
P.S. I can't find a picture of the rear of a Vegas. If it has a fiberglass cover over bumper, I would see if I could build a bracket to attach to the frame and come out just below the bumper. I am a big proponent of "Leave No Scars".
One more comment:
This is my personal opinion only. I have, by observing others' experiences, come to believe that it is best to to do as little messing around with an RV's roof as possible. A little slip can cause a lot of work later.
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