Hi T.W., I recently purchased a model III with the model IV wing upgrade. It came with the factory built wing, 6 gal tanks with a wing locker installed. The locker hinges from the top leading side of locker outboard of the tank. I will try to post a photo of installation for you. I have just started the construction on the fuselage so nothing is covered yet. Good luck.
When we started our kitfox IV 18 Years ago (We are FINALLY finishing it up) My father installed the wing lockers in both wings. I went through the manual and all the documents he used and found the instructions. Looks like they were from a kitfox 3 But obviously worked on our IV. Just verify its the same wing. I'll put the rest in the next reply...