I've seen it mounted off the bumper, but I like the freedom to move the Q around due to wind, etc, so I went for the Weber rolling cart. Would not want to hang the heavy Q off the side of my trailer, but that's just me.
My BBQ mounts off the rear bumper. I figure the bumper is rated to hold 150lbs so it should be able to handle a BBQ. Plus, there's already a gas valve there. I was hoping for something that didn't cost $300.
There may be a bracket, but the Q is far too heavy IMHO to hang it on the siding. Ours goes on the picnic table or on our utility fold up table we carry.