Nutman you raise a good issue. I actually have a small junction box on my roof for this purpose, I got two mending rods and screwed them in and then put a little silicone behind them to hold them away from the junction box, then I just slide the antenna into this gap which holds it securely in place. When I stop somewhere I open my sky light, stand up on the bed, and drop it into the holder. When I leave somewhere, I reverse the process - that way it's not sticking out way above my camper on my drives.
The cable from the antenna runs down into the skylight, which is a little annoying - I guess I could run it somewhere else, but it works for me.