How do some of you mount your racks on camper shells? The last time I mounted the Yakima gutter mount adapters on my shell (fiberglass) there was too much movement and it caused leaking in the window frame. Does anybody have a steel Gemtop shell? Is it better to try and use adapters that mount right on the roof of the shell as opposed to the sides of the shell? Any comments welcome. I am trying to avoid damaging my new shell. (Which I haven't purchased yet) Thanks, Tom