Two things come to mind...
First, would the jiggling and bumping while driving have an affect on the fermentation? I don't know enough brewing chemistry. Some foods and other chemical reactions don't work if they get jiggled. Something about long strands or chemical reactions.
Second, the issue you might run into is having alcohol in the driving compartment. I know you're fermenting...but...that might be enough to get you in a jam. Its the open bottle issue. I've driven vans for a long time. I've asked a few cops how I should take liquor to a picnic. They have all suggested putting the cooler as far away from the driver as possible. Then, pile every thing you can on top. Make it really inconvenient to get to. Even so, if I got stopped for something else a cop could just 'pile on' an open bottle ticket for extra measure...and fines$$$.