I haul a 60# plastic kayak and I have a Yakima "Low Rider" riser assy. It clamps onto the wagon's existing fore 'n aft rails and allows you to use those neato bombproof Yakima cross bars. You could put bikes up there too.

For bikes, I have a thing that I think is called a 'tailgater' that plugs into the 1 1/4" receiver hitch. works pretty good and was cheap (free) too. I pad my bikes from hitting each other with short chunks of those kiddo swim noodle thingys. I strap them to the upright on the tailgater to prevent excessive swinging.

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Never a dull moment at Berry Hill Farm.