I couldn't open the links above so I did a quick search on the sites. I used to frequent them, uhh frequently. I didn't find anything quickly but I know I have seen ways to mount roof racks on top of a hard toneau or a pop up camper. I really like roof racks over hitch racks especially on top of a tonneau because they are out of the way of getting backed into. However they are in the wind more, but on a tonneau, the bikes are partly blocked by the cab. Plus, if you are pulling a camper or other trailer, a hitch mount won't fly.

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