When I had a dock box (don't have one now) I made a crude set of small shelves that fit in the box that allowed for a little better organization. It was nothing my 7th grade shop teacher would have been proud of, but it worked well enough for me.

I have the long low dock box and I use plastic milk crates to store items in. These are used to separate different types of items. However, over the years the stuff has gotten stuffed into the spaces between the crates and on the top.

With no shelves or dividers I can fit my Carry On portable air conditioner in it for short term storage when out sailing. I usually only bring it up to the boat when it is needed. I can also fit in my folded up dinghy (without the A/C).

This is on my list this spring...

I too need to clean and re-organize every 6 months since I do not have shelves.

I have seen other people purchase a plastic (2 or 3 drawers) set from Target, etc. for one side of the box leaving room for chairs and other large objects. This seems to work well for organizing and maximizing space. Doing a quick search, Serilite looks like they might have something that would work.