well, in
MY mind, it would be just using some aluminum angle along the seat edge
and back edge of your deck, cut some square angle to fit your opening.
You may not like it, but, some welding would be involved to really make
a sturdy and lightweight deck / platform that is easy to remove.
some 1" x 1" schedule 40 aluminum tubing welded as a frame would rest inside the angle braces.
Then It would be as easy as putting on flip-flops to put it in or take it out.
of course, you could use 2x4 lumber and plywood - which would be fine if you
don't mind the extra weight.
it's
YOUR boat - so it is
YOUR call
There is nothing more grand than
to be just simply messing around
in an old boat . . . . POGO, 1960