My Safari seems to be a big cell phone signal block. I even have trouble with weak wifi inside. If I move outside the trailer it is often a bar or two better. I think it is the double wall aluminum skin?
I added the Wilson 18" Shorty through-roof RV antenna
. It does not need a ground plane like many trucker antennas. It is mounted on the refrigerator vent cap and the cable runs down through the existing vent hole (no new hole to drill in skin).
The antenna was a huge improvement! I use it for the cellphone and for the ATT Elevate hotspot. So far I've not needed a signal booster. Just double check that you get the right antenna length for your carrier frequency bands.
As Phoenix mentions, phones, cellular modems or hotspots with external antenna connectors work best with the antenna, but you can get a cradle if your phone does not have one.
Once you get the antenna set up maybe consider a wired or bluetooth head set, cordless phone, or speaker phone so you are not limited by the antenna cable.