I chock the wheels with an old towel and prop the wing up on the leading edge and sandwitch it between the side wall and my Bag-O-Stuff that I take to the field.
I have had quite a few planes and quite a few trips to the field and only had damage one time from anything shifting. That was when someone slammed on her brakes in front of me for no reason at all. Put a repairable hole in the covering of the rudder (put a piece of clear packing tape on it and have flown it numerous times just like that- some day I will iron on a piece of monocoat)
I have had far more damage done loading and unloading.