... install a factory OEM tailgate lock matching the ignition key for under $80...installed! You can do that yourself for 40 bucks. I bought the OEM taligate lock for My old truck,about an hour to install, uses the ignition key.
... and cut it to the right length. Then took a drill and made in inside diameter larger to fit over the piece. It made for a snug fit but now my taligate latches like new Would love to see a picture showing how you did that. Good idea. Rubber hose and a tube of silicone can go a long way.