Out here in Aus we do alot of shooting from vehicles, under spotlights. As such I always have the rifle muzzle down on the pasanger seat and if somone else is with me they just rest the rifle on their right leg(right hand drive here!) as it still sits just nice beside the seat. As to loaded/unloaded I always have a full mag, with the action closed and dry fired on an empty chamber.
This means that as I step out of the car i am already loading the rifle this serves two perposes, the first is so much faster to have the round in the spout bolt shut but not closed when the rifle hits the bags. As soon as I'm ready I'll close the bolt tap the bonnet and the ofsider will turn on the light again and two or so second later BOOOOM!
the second thing is the foxes can often hear the sound of the cartridge feeding from the mag and do a runner before a chance for a shot is taken. If anybody wants too see some spotlighting go to youtube .com and type in roo shooting, there is a video of a guy who shoots for a living out of a car pretty impresive stuff - ALL head shots
Cheers
Steve