Are you running it straight in or on an angle? I can load my Xr650L in my '05 Dodge Ram with the 6'5" box on an angle and have about 6" or so to spare. Tie down four corners and close the tailgate, good to go.
I hauled it around like this on my 2 week camping trip, and no issues there or back. Yes, I did lots of riding in between, way more than if I would have left it at home, just saying