I don't know what Lippert uses, probably the cheapest thing they thought off, but in this application they should be using UHMW polyethylene. It's the same material that is used in conveyor belts and snowmobile track glides, very though and very slippery. Contrary to general belief in those applications it's better than teflon and cheaper. Good source for it is McMaster-Carr.
You mentioned 12 feet, that is beyond the typical largest sheet which is 4 x 8 or 4 x 10 feet. Are you sure it's in one piece or is it comprised of shorter lengths.
As you can see you can buy it from McMaster-Carr in different lengths and thicknesses. You might want to check also with a plastics distributor in your area, most of them carry it and they can cut it for you in the size you need.
Great stuff, I use it in my products and on my projects.
On this Smart loader for instance it helps to glide the winch cable and protect the bed edge.
The screws are flat head, hex drive, stainless, tapped into the bed.
Lippert might have come up another "solution".