If you are going to amplify only one device, the Wilson Sleek works well. If you want 4G capability, be sure to purchase the correct model - there are still 3G only versions for sale, as well as some models that are carrier specific. Amazon lists
a model that does both AT&T and Verizon, although not both at the same time (they have a switch to change between carriers).
If you want a repeating system for an RV, only 3G systems are currently available. I have a
Wilson Vehicle Booster Kit, which gives a couple bars of additional gain on both AT&T as well as Verizon as long as you are within 5'-7' of the internal antenna using the Wilson short trucker antenna on the outside. Again, this is 3G only.
Wilson does make a 3G/4G repeating amplifier, however the separation required between the internal & external antennas is way to much for an RV -it is designed for buildings. On top of that it runs around $900.00. There are repeater systems for RVs on the way from companies such as Maximum Signal, but as of this date, not yet approved.