I have the Mopar 4 section foldup on my 6 1/2 ft Laramie I had a 3 section foldup on my shortbed 15.
The 3 section would foldup the back two sections onto the front section and strap down so you could have 2/3's
of the bed open for use. This Mopar one has 4 foldup sections that will foldup and rest on a narrow strip in the front with some stay rods that will fit into pockets so you can have all but about 4 inches of the bed open.
This one sits in channels mounted to the bed and sits flush with the truck box, I haven't had it through a winter yet so we will see how that desighn does with snow and ice. The one on my shortbed sat on top of the bed rails and on top of the tailgate lip,
it did a better job of keeping the water out of the bed the new er one isn't bad biut it does get just a bit of water in from storms or the car wash.
The old one that sat on the rails and tailgate would freeze down on the tailgate. I keep it liberaly lubricated with a silicon spray lube and it was always easily unfrooze with a narrow bladed putty knife that I keep in the trucks door pocket for that purpose after the first time, that was on a 15 which had a small whales tail on the tailgate top which held water when snow melted. My 19 is flat on the tailgate top.