Doesn't quite deal with the dust, but one reason SUVs are so popular is that you can carry dirty gear in them with just a simple well padded cargo cover (although not sure if dust would be an issue flowing over, in our use case never has been). I have a truck, but I haul things that are often dropped off on a pallet and is loose like loose mulch and the like and needs to be dumped or that is too oversize to fit like I just moved a couch and mattress and box spring this week, but that's what an OPEN bed is for.
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If I had to get a topper, I'd get one of those collapsible toppers, as that's something an SUV can't do: