Milk Crates
Milk Crates, the good ones that you get from the milk truck guy when you offer to take him sailing, not the ones that you buy at the hardware store.
A couple of pieces of light plastic, which is flexiable thin stuff.
Zip ties.
A good knowledge of some basic knots to make a bridle.
Cut the plastic to fit the bottom of the milk crate, place the plastic in the milk crate. Punch holes in the edges of the plastic allowing a good margin for strength. Zip tie the plastic to the bottom of the milk crate. With a sharp knife cut the plastic on the diagonal from each of the four corners to the corner diagonally opposite it.
Tie the bridal system to the top using some STRONG knots and GOOD Fairly non stretch line.
Hang outboard on spin poles etc when you want to use them. When you don't organize that aft locker space using the milk crates, just don't mess up the plastic.
Guy