i had a friend who had a sirius in her pt cruiser, the antenna was routed through the vehicle, under the moulding for the door sill, and behind the back seat, then ran up under the interior moulding for the back and then slipped through the weather stripping (where it came back together) and then sat about 5-8 inches from the opening.
my buddy has i think an xm radio antenna in his wrx somewhere, im meeting up with him on saturday to do some struts, ill see how his antenna was run.