I have a hard enough time trying to keep my VHF/UHF and CB whip antennas attached to the truck when on the trail. I keep my screwdriver in the back of the truck with a tripod mount that I can deploy quickly when stopped, but am always looking for mounting ideas to go mobile HF.
I just might have to fab up a mount to keep the coil centered and below the roof line. I've bent my VHF/UHF antenna a few times mounted on the back corner.
With my current setup I'm good from 10m to 80m but if you add a Cap-Hat and/or a longer whip you don't have to use as much coil to get 80m and should be able to get a good SWR on 160m.