Installed my American Tonneau Company soft tri-fold cover. I know it's not the best but it's American made and couldn't beat the sale price (plus it came with a tailgate seal).
I've had fiberglass tonneaus for almost 20 years and have had an open bed on the RAM since I bought it. I wanted to split the difference and have a usable bed but be able to cover it. This is much nicer than trying to maneuver a 7' x 5' slab of fiberglass around whenever I want to use the bed.
I also did not want any rails, mounts, or clamps that would damage the lip of the bed. This fits the bill, is easy on and easy off, won't protest if I articulate off-roading, and is a fraction of the cost of a hard tri-fold.
The cover...
My "custom" tailgate seal...
It's not going to keep everything out but good enough to keep most of it out.