I have yet to find an antenna mounting idea for HF operating while in motion.
While parked or camping, More to See has good suggestions.
My short time parked setup is 3/8"x24 mounted to mirror, Hustler QD-2 Quick Disconnect and Outbacker or Outreach antenna. The main goal is to get the feedpoint connection near or above the roof. The coach ladder really allows several mounting possibilities, but another support is the tow bar receiver and a pedestal to raise the feedpoint of the antenna.
For longer stays, I use those same antennas with a tripod mount independent of the coach or get permission to string up a Buckmaster OCF dipole.
My camper is a Super C, Freightliner Columbia chassis. I lucked out this time...the 3/8"x24 mounts came installed in the top of the mirrors from the factory. Truck stops have all types of antenna mounting possibilities. Most universal antenna mounts include the mounting hardware and are a good start.