Replacing dart 18 shroud plate

Working on my dart 18 today when in noticed that the port side shroud plate was loose. When I went to tighten up the screws, two out of three will not tighten. I assume there were nuts on the inside of the hull that have rusted out. I am afraid I will need to cut a hole in the deck to access and repair this. Anyone have any experience with this type of repair?