I did the same install. I routed the wire from the radio, through the engine firewall to the right hand side of the frame. Then up through floor on the right hand side of the door. Then follow the LED/awning wiring up the awning rail to the roof. Then under the drip rail fwd, the mount the antenna on the front cap. Been working good so far. You'll have to buy 10 ft extension cable and splice into the factory antenna wire. Just cut the end off the factory antenna and route from the roof down. It'll get you to about the battery area. Then cut the correct end off the extension cable and route from the cabin through the bulkhead to the battery area. Soldering the XM cable is pretty delicate, but wasn't too hard. Just make sure to solder the overbraids together, and the inner conductor together, but keep them separate once you heatshrink everything together. Might not be the easiest, but its the way we did ours. Hope it helps.
I bought this extra cable.