Alternative
Robb,
If I may offer an alternative, check out any one of the several excellent flying apps that are available for tablets and combine it with a portable ADS-B receiver and you won't even need an XM subscription. Stick it on a kneeboard, a RAM mount, or just leave it on your lap. A few of the bigger names:
ForeFlight (What I use. iOS only)
WingX Pro (iOS and Android, but the Android version is comparatively limited)
Garmin Pilot (iOS and Android)
For hardware, on the iOS side, nearly any available iPad will run the above software. I will say, however, that the iPad Air 2 and the brand new Mini, as well as the new iPad Pro have an antiglare coating that makes the screen far more readable in an RV bubble. I have an Air 2. I find it a bit large for the cockpit and were I to buy another, I'd go with the new Mini.
On the Android side, lots of folks love the Google Nexus 7. There are two models. The newer one has a much better screen and was released in 2013. Here's an
Amazon link. It was released in 2013, which means it's getting a bit long in the tooth hardware wise but that also means it is a SCREAMING deal. I don't really follow Android hardware releases very much, so that's about the extent of what I know people have successfully used in the cockpit but I'm certain there are other, great options out there.
KF