I mounted my sirius antenna using its magnetic base on the steel structure of the strut bar and covered it with the strut bar's plastic cover. This way, it's completely out of sight. The concealed antenna works as well as the one on my Volvo wagon's roof. I suspect that the XM antenna would perform much the same way.

 

+1. Had mine mounted there for a year and a half and havent lost the signal yet. Have it mounted right next to my GPS antenna and they both work great plus it made it very easy to install.

 

Really i had a huge problem with the Sirius antenna on my strut bar. I'm working on the install now, and I reluctantly had to put it on the roof. I got very sporadic signal with it on the strut bar (that is to say it really didn't work at all). With the antenna on the roof now it's perfect signal always.

I guess it could be my area, or the dark tint on the hatch. Although now I'm thinking maybe I'll try putting it at the base of the windshield infront of the guage cluster.