It has been quite a while since I have put removable floor boards in an aluminium boat. But I will tell you what I remember. Determine the height from the floor you want the floorboards to be. Instructions are for one section only, rest are similar. Cut two pieces of 1x4 for the section that you are going to install the floorboards in and cut them to fit two to three inches from the front and back of the section (between the seats) but not directly over a rib, and at the height you want. Cut a cardboard template of the profile of the hull under the inner edge of each 1x4. Holding it against the 1x4 mark a line along the cardboard aligned with the top of the 1x4. Make sure the bottom edge is as close to the floor as possible. Transfer your template to a 2x? so that it aligns with the bottom of the boat and the top of the 1x4. Scribe a line along the top edge of the 2x? but do not cut it at this point. Using rubber matting of at least 3/8th" cut it so you can fold it around the 2x? in 2-3 ft " strips around the bottom of the 2x? , leaving a suitable gap (1-2") down the centre line between strips to allow for water transfer between compartments. Secure it along the folded edge with glue and screws. Do not use any screws along the bottom edge. You do not need the matting to go up the sides. You could even cut out a small section of the 2x? in the centre to promote more water flow. You do not want the wood touching the bottom of the boat, that is what the matting is for. Again scribe a line along the 2x? so that it is level with the edge of the 1x4, and cut along that line. Secure the 2x? to the 1x4 using a good waterproof glue, stainless screws and clamps. Repeat for the other 1x4.
Put the two pieces you have just made in their positions. Measure between the 2x?s and install a couple or more cross pieces of suitable dimension, but be sure they do not touch the aluminium floor. Cover the framework you have just made with 3/8th plywood. prime and paint with a good enamel marine paint, sprinkle some dried beach sand into the wet paint on the surface you will walk on for non skid.
Because of the chemical reaction between pressure treated wood and aluminium, I would not use any in this construction. Use only stainless fasteners.
I hope this makes sense to you
