My dad and I worked on our 18ft jon boat that we bought this past summer, and we also made a deck, but we only put our battery charger for the trolling motor under it, the rest is for storage.
I was curious tho, if anyone had ever built a deck the same way we had. we made two braces, at the front end of the boat where it rises, and at the front of the first seat, then we hung 4 floor joist hangers on both sides, and used 2x4's to make it level with the seat when a piece of half inch plywood was put on top of the joists...we did it this way to keep the boat as light as possible, while still making a good size deck....(it's 8x5 ft....) anyway, i was just curious about people's thoughts...i'm not sure if it'll work, but i'll try to attach a picture in case anyone was curious to see how it looks....
tight lines