Yeah that's why I mounted mine to the existing old crank up air antenna. Metal acts as a ground plane as well as having the added benefit of using the existing coax ran down to the panel behind the TV providing adequate distance between the two antennas.
I mounted my Wilson RV antenna to the side of my Fantastic Ultra Breeze Vent Cover. It's the highest point on my PUP and luckily perpendicular to the roof. I don't drive with it attached, I installed/uninstall with each setup.
I tried a zboost 560. My local dealer carries them and gave me one to try before purchasing. Works really well. Had to use a directional antenna versus an omni to be able to get out but have 3 to 4 bars. My children can contact us now. We will wait to see if that is a good thing .