He have 2 800XPs with portable XM. First one, like DrProc mentioned, the antenna is placed in a small clear plastic basket stuck to the side windows. Reliable, yes and no! It requires moving it from one side of the aircraft to the other depending on the direction of travel (east and west). It needs to primarily facing the south to west direction for a good signal. Take note, some of the bigger cities while on the ground have a ground based transmitter of somekind that you can actually receive while still in the hangar. Our second aircraft, we opted to put an external antenna (combination XM/GPS) in over the cockpit with the terminals in the cockpit to connect to the receiver. This option works, by far the best. The ACARS/AFIS/Datalink (whatever you want to call it) is expensive. Just depends on if you can justify the entire package, not just the weather (includes PDC, D-ATIS, Oceanic Clearences, Messaging capabilities to office and/or data service provider for flight plans, etc). If you go to many larger airports where PDC is available, then you can probably justify the expense. Good luck to you!