Provided you do the Job correctly it will not damage the chassis and as I have mentioned before on how to install one, top hole in your van is bigger than the bottom hole, the bottom hole in the chassis is the same size as the bolt your using and the top hole is the size of a small steel tube (available from any fabricator) so long as you bolt fits inside it, drop the tube into the top hole and put your bolt through it, this stops you deforming the chassis.
Put your star washer on followed by the nut, (you can add a small spreader plate if you wish) tighten only the bolt and not the nut, this will pull the star washer into the chassis and create little dimples to stop the nut coming undone.
Use only high tensile steel nuts and bolts, there cheap enough.
If you fit using the above instructions you'll have no problems, don't forget thousands of cars & vans are fitted with tow bars and all fitted to the chassis with no problems.