Here is a picture of us loading a 10 x 12 shed on an 18' car hauler this past Sunday. I didn't get a final picture of it in position and all strapped down, but the straps stayed tight the whole 70-80 mile trip.

did you have a cribbing or blocking to keep the weight off your fenders and to keep it from mashing them up im sure u did or they probly would have been pressed to the tires the whole trip.