We are gonna skip the seats since I was using a crummy camera for the seat construction. The seats are identical to the top of the motor box so consider it the same only smaller.
So the box was built out of 1/2" plywood in two pieces, a three sided lower portion joined to the floor and transom and the top with is three sides with a top that will flip forward to access the engine. The entire box is covered with vinyl with a cushion on the top. The top portion of the box was probably ok to reuse the wood but I replaced it anyway. The lower portion of the box being on the floor of the boat got wet much more often and was rotten in the corners and other areas. So... using the old box for measurements I started my plan. I had Home Depot cut the plywood into strips along the length of the panel to make it easier to move and reduce my cutting needs since I did not have an eight foot saw guide. So I really only had to cut these pieces to length.
To assemble the box I frames some strips of pressure treated lumber about 1"X1.5" I had lying around and used 1" staples and tightbond II waterproof wood glue to hold it together tight.
Once assembled I did a rough sanding to remove splinters and break the edges for the vinyl. Once sanded I put two coats of Sherman Williams exterior latex paint over everything.
Once the glue was set these boxes are very sturdy and once they are joined to the boat this thing is going nowhere!