Just went out to garage, and verified that my mx4 completely clears where the uprights would mount on the rails. You need to verify that the actual rack has 16 inches of clearance above the rails for the panels to clear. Good luck with finding something. Hope this info helps. Fwiw I like the fit and quality of the mx4.
I am also adding to hope someone has found something! Everything I’ve seen so far seems to need to clamp into the bed where the uprights would mount. It seems like the cover wouldn’t close with the mounts in place.