After getting my new GS430 and making an appointment for XM install, the dealer talked about mounting the antenna on my trunk lid. No way I was doing that so I found this site and had them put it under the back package tray as mentioned here. Sound is great and just a couple of minor dropouts under low, long underpasses. The first one my dealer did like that. Transfered my XM with two years prepaid left to the GS from my 04 TL.

 

Is there a reason why they can't put the XM antenna wherever the GPS antenna is?

 

The GPS unit is on the front windshield above the rearview mirror. They'd have to run the wires from the trunk to the front.