I just finished a rebuild of an 18' open bow Lund. I coated each board (all sides) with Durabak for the reasons Steve mentioned. Fiberglassing the boards seemed like a lot of unnecessary work. This is my first season with the rebuilt boat, so no information on durability of the Durabak. I love the non-slip properties. I wish I had filled the hull with water as suggested here. I did a visual inspection for a small leak I have, but found nothing. In hind sight, I wonder if I have some water logged foam under the floor boards. My flooring was 1/2" in the bow area, and thicker at the back of the boat. I replaced it with marine grade of the same dimensions. The two layers of coated 1/2 inch as mentioned would be rock solid, but in my opinion adds a lot of unnecessary weight and work. Save as much of the old wood as you can for templates. Even then, it is a lot trial and error fitting and trimming. Build the whole floor of bare wood and test fit it in the boat, before you commit to fiberglass or durabak and screws. Make allowances for the thickness of the finish at the joints. Do the same assemble first process for your consoles, bow storage areas, etc. I found the worst rot on the vertical pieces of wood rather than the floor. I lost 1 1/2 inches to rot on the bottom of my consoles (walk through windshield). It was held together with the carpet used to cover the old wood. I'm sure the rubber backed carpet trapped in moisture and contributed to the problem. I bought the boat used, so I don't know how it was cared for previously. It looks like it spent a decent amount of time outdoors. I hope the coating of Durabak I gave it prevents that in the future. I replaced all screws and nuts with stainless steel. Jamestown Distributors has an online presence and had everything I needed. All nuts have the nylon insert to prevent vibrating loose. Good luck, keep us posted.