I'd say that to keep it in your line of sight the two best locations are either just above the radio (you'd have to pull it out to see if there is any room up there to recess-mount it. If you replaced the factury headunit with a single-DIN aftermarket you might have the perfect amount of room for the SG
Or you could mount it to the dash on the far left side where the dash dips down. Depending on your eyesight you could push it all the way forward so that it meets the windshield.
Here is where I currently have my Sirius unit mounted.....
-Tim
2006 Mercury Mariner Hybrid AWD
Black with Pebble interior
Premium Package with Nav & Moonroof
Current ODO:
26,152
Typical Drive: 20 min crosstown in heavy traffic (3.5mi there and back twice a day)
532 Gallons of gas saved
That's 10,642 lbs less CO2 emitted