speaking of 80/20 material used on roof racks...Prinsu Design Studio builds some great racks using 80/20. I have one on my Land Cruiser and it's fantastic. Other than fasteners it's 100% aluminum so it's super lightweight but very strong. The price is really nice too at just under $900 for the one I have on my FZJ80
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The OP would likely need to do something custom to work on top of the van but maybe this give some ideas for what can be done.
Nice, wish they made one for my 5th Gen 4Runner.