Several years ago Pioneer offered a neat unit called Inno. It had an enclosed battery, so portable. But you could also get home and vehicle cradles. We have two of them plus cradles in the car, truck, and RV. It allows us two subscriptions and still be used in four places. The neat thing was that it also had the ability to record music. This is great when traveling in places with poor or no reception and still have music. I think that XM/Sirius still offers a version of that unit sold as the Roady. If we were shopping for a new unit, guaranteed that would be my choice.
As for the radio antenna? Is this a class C? Then yes the antenna is in the wrong place. In the old days people used to mount a second antenna on the roof of the RV and run the wire down and attach it to the original antenna with an alligator clip. Seemed to work then. Personally I would mount a new ground plane antenna up near the roof and figure out how to get the wire down to the back of the radio. Usually can be done after a fashion.