Use Ordinary Flooring
or if that is not obtainable use ¾-inch pine boards, and run them lengthwise from the bow to the front end of the cabin and along the sides of the cabin. Then floor the cabin lengthwise from bow to stern. This gives you a dry cabin floor, for there are 4 inches of space underneath for bilge-water, which unless your boat is badly made and very leaky, is plenty of room for what little water may leak in from above or below. The two side-boards of the cabin floor must, of course, have square places neatly cut out to fit the uprights of the cabin. This may be done by slipping the floor-board up against the uprights and carefully marking the places with a pencil where they will come through the board, and then at each mark sawing two inches in the floor plank, and cutting out the blocks with a chisel.