You will not want the dingy catching air over the top of the roof or be wider than your van - You would be surprised at the wind force created at highway speeds. Think about how low you can hang a basket without scraping from a driveway pull out and add 8' to that - This will tell you if your van roof will be tall enough. Most cargo carriers are rated for 500 lbs, but you will need to check your receiver for the hitch weight rating. You will need to use to some type of wobble dampening device on the carrier and create some additional tie down points higher up the rear of the van. As long as your overall height is bellow 13.5', overall width is bellow 8.5', your signal/auxiliary rear lamps are clearly visible and you have left and right exterior mirrors, you are legal.
