I've spent lots of time working and driving, and have yet to have a situation where my seatbelt inhibitted my draw. Lean forward, shift slightly left, and draw; NBD. I've done this drill literally hundreds of times in training, both from the driver's seat and passenger's seat - never had a problem. You WILL, of course, most likely "laser" your right leg during the draw and pivot, so Safety Rule #3 is paramount here...
Crossdraw is more convenient while seated, no doubt, but doesn't conceal as well, for me, so isn't worth the effort of putting on and taking off holsters. A "Driving" holster would be theoretically ideal, but I don't have $100 lying around for a good one, so I just make due...
One thing I did learn, the hard way, was that changing carry locations to suit vehicle use/dress is NOT a good thing. One one pretty hairy occassion in Haiti, when the crowd was getting restless and shots were starting to ring out; both my partner and I (lifelong strongside hip holster guys) were slapping our empty right hips looking for our pistols, forgetting we were using shoulder rigs over our BDUs...
YMMV, of course...
Regards,
Kevin