Tarps get shredded by the wind at 70 mph and will quickly be part of the roadside trash. I keep my boat rigged and on the trailer and accept that I'll get crappy mileage when I haul it. But it's a lot easier than derigging and putting it into the car (if there were even room for drybox, cooler, gear that lives on the boat, etc.). Plus I toss lots of gear in the boat when traveling.
The last time I rolled my boat was when PRO took it down to Lee's and brought it back up from Diamond. Then I inflated it, rigged and headed home.
That was waaay too long ago...
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse