Retractable Bed Cover with full length T-SlotsTracks?

Both Yakima setups have a 500 lb capacity if mounted directly to the bed, but it's cut down to 300 lbs if you use the t-slot You can see in

RetraxPRO XR Tonneau Cover Highlights: Supports up to 500 lbs evenly distributed Compatible with most T-slot accessories from Rhino Rack, Yakima, Thule,

tonneau covers with tslot tracks cover by combining the Trax Rail system with the t-slot accessories Product Features Low Profile Design; Increased Cargo Capacity Above and Below the Cover

siti slot machine BESTWYLL Electrical T Slot Pickup Truck Bed Electric Retractable Tonneau Cover for 2012-2021 Ford Ranger Xlt Double Cab E-K04, Find Details about Hard