my old 1999 2500 HD, I used Green Treated 2x10's, cut to fit in the slots.
Round the bottom corners. so the boards fit snugly.
Run a 2x10, along side each wheel well, creating an "H" Pattern.
Not that heavy, to remove and install, lean against the out side of the garage or shed, when not used. Winter, it holds just enough sand, to really give the truck a nice ride. Slap a green treated 4x8 over the top and you still have your truck bed to use.
For this little 1500 ii got now. been thinking about oen of those flip bed extenders for cargo seperation. DOnt; do much anymore, reason I went with smaller trucka dn short box.
good luck to you and let us know what you end up doing
might be an idea another oculd use, down the road.