Looks like the Ram sprung a leak, losing diesel @ a pretty good rate-anybody ever repaired a plastic fuel tank? I can probably get a new oversize one for $1200 or so, or roll the dice with a junkyard one, anybody ever had luck fixing one?
You might be able to get a Spectra Premium brand tank for less, however, I don't know how good they are.
Be ready to get new tank straps when installing a tank. I often find that even if a car has never been exposed to road salt, the straps are still prone to rust, and crack when being removed.
If it is just HDPE see if there is a plastic fabrication shop in your area that can thermally weld it. I have found many of these to be UHMWPE and you would be out of luck if that is what your tank is made from.
Nylon? Wiki says HDPE.
"Plastic high-density polyethylene (HDPE) fuel tanks made by blow molding."
You're correct. I assumed that because Nylon is used in the fuel system that it was used for the tank but I am incorrect. They use a multi-layer (up to 6 layers) system with HDPE on the outside and other materials on the inside to reduce permeability.
I don't think you can do any trustworthy repair on them.