Here are a couple of under cockpit storage bins that are pretty straight forward. I made the starboard one last year but took it apart this winter and shaved another inch off the width. This leaves a gap between the bin and the quarter berth that is just right for stowing the hatch boards when getting under way. I don't even have to climb down into the cabin to put them away.

I used 1/2" Baltic Birch from the big box store for the starboard bin. and the end panels of the port one.

I used 1" extruded foam isulation in a sandwich between 1/4" plywood sides on the port bin so it can be used as a cooler when cruising. This bin is coated with epoxy and has epoxy fillets at the seams so it is completely waterproof.

Yes, I did add a drain to the bottom of the cooler. I over drilled the hole and potted it with epoxy before installing so the insulation will not be contaminated with funky melt water.

Both bins have a 1 x 2 runner on the inboard bottom to keep them level, compensating for the slope of the cabin sole. The runners have a strip of HMPE plastic underneath for easy sliding.

Partial lids allow the bins to be used as steps when pulled part way out. This is really helpful as it allows a short guy like me to work the mast while standing in the cabin. I did make a fully insulated lid for the port bin for use as a cooler when needed.