I had the same problem after installing my Gobi Stealth. The Gobi fairing effectively blocks the signal from the XM antenna most of the time.
My solution was to use another XM antenna at an alternate location.The antenna that I chose was the Terk XMicro2 that I bought from Crutchfield
http://www.crutchfield.com/p_209XMICRO2/Terk-XMicro2.html?search=terk+xm+antenna
I had to do a little modifying of the antenna's Fakra connector with the addition of another slot.
I ran the new antenna wire out the side of the dash, up the inside of the door gasket, behind the A-pillar trim, to the roof.
The base of the antenna has a very strong magnet, and the antenna stays where you place it.
I chose the center fairing bracket as a nice flat, exposed location.
I now get good XM reception, with very, very few times of a momentary blocked signal.