I had a Metzler boat,it had plastic tubs that went from pontoon to pontoon (across) had a seat on it and made for some dry storage.You could easily make something out of wood.
I also had some rubber mounts glued to the toons,this made it easier to attach things too like rod holders and fish finders.
Theres a shop in town here that deals with inflatables check them out, very friendly people.I can't remember their name.