Most of the camping I've done, I've dumped everything out anyhow.
The more I consider this, I think that a canopy on spring rollers that could be pulled out and have struts back to the side of the car or down straight would work out better. Am sure that anytime set up, would hang extra tarp's off end and sides for some wind damping. The whole unit could be fastened to any type of existing rack and moved between units as needed. Had something like that on a motor home several years ago. I've even seen some advertised on TV for the back patio. Have to be a lot smaller scale though.
The unit pictured is a bit over $1000 with the rack and canopy. There is one for Jeeps called a "Dave's" rack but it folds back over the back. Have heard bad things about it, quality of material, manufacture, rust, road noise. Its about the same price.
Where I live, having some cover from the sun is nice, cover from the rain even better.