I went with the WILSON SLEEK CRADLE 3G setup three or four years back mainly for my Verizon MIFI 2200 unit. This came with a small antenna which I have mounted on the roof of my OFF-ROAD POPUP. This is my docking station for the MIFI 2200 Mobile HOTSPOT unit providing WIFI to my tablets and devices when we are camping off-road.
I was surprised that the CRADLE also become an passive indoor antenna for my cellphones. Of course sitting my cellphone in the cradle really boosted the cellphone signal.
I got the same type of operations inside my truck for a temporary setup. The truck would be more like your MH setup I guess being all metal... Again the Wilson cradle provided as an indoor antenna for our two cell phones..
Our cell phones are with VERIZON which seem to work great coverage wise for us when we are way off the beaten paths away from the Interstates...
Roy Ken