Isn't it customary to use stainless steel fasteners on the outside of the trailer? I have a mixed bag of stainless and non-stainless fasteners on my Bigfoot 21RB. Some of the non-stainless ones are beginning to rust and leave an ugly stain on the fiberglass. I've already changed some of them.
was pretty bad about using zink coated screws on the exterior of their trailers. They do rust if you give them enough time. I replaced all the exterior screws in my Bigfoot with stainless screws. I purchased my stainless screws on line from this outfit:
I ordered several different sizes and lengths because there are several different sizes used on the trailer. Check all your sizes before you order. They have them in the square bit drive. As I remember they did combine shipping.
I replaced the old screws one at a time. I would remove one then dip the threads of a new stainless replacement in RV caulking and install it before removing the next old one. You do not want to take all the old screws out at one time because the part they are fastening might fall
off. I used a hand screw driver to be sure I did not over tighten and strip out the fiberglass. It was an easy job and did not take very long.