Paul, your skiff is the same as mine. I took a 4'X8'x3/4" sheet of pt plywood and cut it right down the middle. 2 feet wide and 8 feet long.
With mask on I sanded the edges, primed with exterior primer and rolled 4 coats of Krylon Camo paint front back and sides.
Took 1 inch sheet metal screws and screwed right through it right into the floor ribs. Like a rock, very stable and no rot. Each spring I give it a topside touch up in camo. last spring I took the seats out and the floor and no rot yet on the floor. Just a quick sand and more paint. You can make a wider floor in that Mirrocraft but your level of your feet will be higher than the water line which makes your skiff more unstable.
Simple and it has worked really well for me. Seats are affixed to the floor with 1x1 al angle.
Hope that helps, after all it's only a skiff that is going to be covered in mashed sandeels and fish poo right?
