I have one of these WILSON SLEEK CRADLEs setup that I use in my truck and also inside my POPUP trailer... This is an older unit so doesn't support the high end cell phone bands...
I got this to use with my VERIZON MIFI unit which allows me to sit the MIFI unit in the holder and it connects to the outside via an external antenna... The back part of the cradle base is a passive antenna that would be sitting next to whatever you have sitting in the cradle.
This passive antenna also produces a small cell phone inside antenna zone doing this...
Helps with my cell phone usage inside my trailer or inside my truck which is totally metal enclosed...
A WILSON TYPE Amplifier designed especially for giving you a repeater type cell phone signal would be the better thing to have... Just passing this CRADLE info on as it does help somewhat inside you trailer or truck. Reall works great if you have your cellphone placed in the cradle right up against the passive antenna in the back of the cradle holder.
You will want to get something that supports 2G-3G-4G cellphone operations...
Roy Ken