I routed the antenna wire under the dash and up the center post in the windshield in our Itasca. A large part of how you route the wire will depend upon what you have to route it in and behind. You could if necessary use a stick on wire chase.
You also need a place for the antenna to mount. I used the blade from a large metal spatula that I managed to slip up into the overhead structure. It got me well up under the fiberglass roof with nothing else in the way. It was a FUN job, but it worked for 7-8 years. Actually thinking of doing it again in our new rig. Why pay the $$$ for two? I can get a modern XM receiver and use it in my car, the Toad and the RV all for a single price. Save a bunch of cash. We don't listen to the radio too much when parked, usually just while driving.