You can't bring your CO2 tank along for the ride? I don't know what size tank you have, but my 5# tank is fairly portable. My 20# tank, on the other hand...
In my experience, most of my kegs take a bit of pressure to seal properly. I can just see the keg slumping over in the car seat and leaking slowly for the duration of a 45 drive. From an oxygenation standpoint, it depends if you are planning to put a full 5-gal batch into a 5-gal keg. If so, the headspace should be minimal, and an overnight stay shouldn't really be problematic. If you are only filling the keg halfway though, there will be a whole lot more oxygen to slosh around with the beer during the drive, so it might taste like wet cardboard by the time it gets home to the kegerator.
Before I began kegging, I purged a few fermenters using dry ice. This might also be an option, (or just clean, sanitize, and purge before you go as someone else said) but I'm still wary of leaks. Just my $0.02.