Recently mounted a Proxicast antenna to boost signal in the van and am posting in case others are interested in doing the same. The full plan is that I wanted a cellular hotspot in the van, but decided to use an antenna to maximize ability to connect. This will eventually connect to a Cudy AX3000 acting as a Wi-Fi cellular hotspot.
The antenna is 4x4 MIMO unidirectional and is about 3.5 inches tall and 2 inches wide so very unobtrusive. I decided to mount on the plastic housing that contains the backup camera. Antenna mounts with a .5 inch hole. I used a washer and of course loctite to secure it. The entire antenna bottom is adhesive and seals to the top completely. I mounted slightly off center thinking it might interfere with the brake light, but there is likely more than enough room.