I am also a XM/Sirius satellite radio junkie, too, and have one in each car and one at the house, but not one in our TT. However, having installed these myself, I UNDERSTAND your issue well.
Probably the easiest solution is to run the cable under the rubber around a slideout if you have one. But, since each RV is different, you will have to find what works for your situation.
Other ideas include:
1. Routing up through the shaft of the crank-up TV antenna. In our case, the TV antenna is located above the MB, so the cable would have to protrude out around the hand crank cover. That might not be the best option but would get the antenna on the roof in the right spot.
2. Going out via the A/C compartment. While this is normally sealed up pretty good, there are spots where the wires come through from above that might allow you to route it there. This also leaves a visible wire at the A/C grille on the ceiling, so it is not optimal either.
3. Going out through the back of the fridge compartment. This will be difficult, but not impossible to do.
4. Route the cable alongside the main 12V power cable to the battery. Normally, there is a chase for this that you can follow. This may be the best option for a permanent situation, since the cable will not be visible when you are done, in all likelihood, however the satellite radio will likely have to be installed in the MB area.
I guess the real issue here is that there aren't supposed to be a lot of "holes" in your RV in the first place, (or your trailer would get a lot of bugs inside), which you need to route that cable and its connector through. But, this is the same situation with a car, so you'll probably find something that works for you.