Being a conversion van I probably would not want to mount one of the crank up antennas as well.
In my OFF-ROAD POPUP I had similar thoughts against drilling through the roof so I went with a side mount on a pole antenna setup. Granted when the POPUP trailer roof is raised I have a couyple of pretty strong mounts to the side of the trailer that makes it pretty strong. I experimented with the various antennas to put on the pole and it ende up the BATWING turned out to be the best.
Well I will take that back a notch. The best was actually one of those $90 full yagis from Lowes and it was great picking up up both VHF and UHF stations. It extended out over both ends of my POPUP trailer and would hit trees when rotated haha... The problem was however I destroyed it in one season having to take it down for transport after each stay and things broke and had to get rid of it.
Then I went to the BATWING and the Kings JACK antenna on my pole.
The BATWING ended up being the better of the two for me as I did need some beam width that BATWING gave. The KINGS antenna had to be really close to the direction of the HD TV station to pick it up at any long distance away...
My install would work great from a bumper mount and a support on the roof side of your setup.
This is what my BATWING mount ended up like... The ceter section allows the antenna pole inner section to be turn while the outer is secured to the roof mount. I can reach thru the trailer window flap to move the roof mounted BATWING if necessary...
We get great full blown High Def TV from the local towns using this setup. It is also easy to take down and put up and only takes about five minutes. No hole in the roof... It breaks down in two section for the pole and the batwing antenna removes from the pole real easy. Our whole thing sits inside our central area for the POPUP when lowered down for transport...
Being using this setup now since about 2010...
Roy Ken