Several years ago, I bought stainless-steel clutch-head rear fender bolts. The main vendors do not sell them now. Zinc-plated stainless clutch-head rear fender bolts are readily available.
Note what Denny posted about the fenders being bolted to the bed before the beds were painted. The zinc-plated clutch-head bolts would be sealed with paint and, with care, would last a long time.
