I move my Sirius unit back and forth between my Jeep and my motorcycle. When I put it in the Jeep, I just toss the antenna out into the middle of the hood behind the footman loop. Run the wire through the gap where the windshield frame meets the body and I'm golden. You're right about the dead spots under drive-through canopys, and also a couple of spots coming down my driveway have heavy tree canopy coverage that'll kill the signal too.
-- Old Crow "Yol Bolson!" '82 FLTC-P "Miss Pearl" '95 YJ Rio Grande BS#133, SENS, TOMKAT, MAMBM