I have use a wilson sleek for my tow vehicle - it provides enough boost that at my house I go from 1 bar to 3-4. This device requires you place your phone in a cradle so you will need a bluetooth headset to use it.
I also added a wilson rv antenna to the coach which has a built in ground plane & gives me a 3db boost over the stock Sleek antenna.
It depends on you to go with your needs and analyze which best suits your condition. There are cradle and wireless antennas are available too. Go with something that you need to implement.