To wax a bolt and the largest fender washer I can get. Then I make up a pad of fiberglass mat with a hole in it to pass the bolt through. I saturate the mat with epoxy and slide the bolt through it so that the glass mat is resting on the fender washer. Then I put the bolt through the hole with the mat on the uneven side and snug the bolt down to compress the mat a bit. When the epoxy kicks take the bolt out and you have a nice flat, smooth bearing surface.