I have a Clarion radio/CD player in my R-25 so I don't know if they're similar but here's how I set mine up.
I have an XM receiver and bought car kits for my R-25, my pontoon boat, my F250 truck, and a 99 Corvette. The car kit is wired into each one, with a standard cable that outputs the sound to the auxiliary ports on the various radios. The Clarion in the R-25 has two auxiliary ports, one on the front of the radio and one that's on a wire hanging from the back of the radio. on the R-25, I added a 12 volt adapter inside the glove box, mounted the car kit XM dock on top of the dash on the port side and ran the wires for power and the audio feed from the auxiliary adapter down into the glove box. I put the small XM antenna on the shelf that houses the lights over the dining table and routed the wire down by the window frame on the passengers side, through the glove box and up to the XM receiver dock for the car kit. The reception seems to be fine through the top of the boat.
What's nice about this setup is I just move the XM receiver to the boat/car/truck that I'm using. When towing the R-25, the receiver is in the truck and when I launch the boat it moves to the cabin. one subscription for 4 vehicle/watercraft.
Hope that helps. Any questions email or pm me.