With the hull now the correct way up the next stage was to offer up the tubes and mark round them on the deck. Make sure that they are fully inflated and tack them in place with a couple of tacks. You use the line of the tubes on the deck to place the outside edge of the side rail box sections. Take extra care around the curve of the bow, if you get this wrong the tube will not fit correctly later. The height of the side rails is the next measurement you need. I found this is not supplied in the plans. You carefully measure from the deck to the side flange of the tubes, I cannot stress enough that the tubes must be blown up hard at this stage. If they are not there will be an error in your measurements.
Once I was happy with the line I removed the tubes and packed them back up for later. I then cut the ply for the inner and outer skin of the sides. I just cut the sheet into equal strips of the correct height. I then screwed and glued the batten around the line I had drawn on the deck from the edge of the tube. Make sure you allow for the thickness of the ply sheet before you fix the batten. I then screwed and glued the inner sheet of ply to the batten. I cut and fitted it as I went round the hull. I started at the stern and finished each side at the bow. I then screwed and glued the top batten in place. I used a wider batten on the stern section than recommended on the plan so it would be stronger for a heavy engine. I then filled the side with polystyrene sheet and fitted the outer ply skin.