Easy to make
I just made a new 3 piece door for my C22. I used 1/2 inch plywood that I found in a garbage dumpster. It was exterior grade plywood, with a good veneer on the one side. It had been painted for use as a sign on a construction site of a drug store being built. I used a piece of it to make a one piece companion way door for my '76 Neptune 16. I painted it with rustoleum and 5 years later, it looks as good now as the day I made it. For the C22, I made the door in 3 pieces for easy storage below. I have a table saw to work with, but a circular saw and router would suffice. I started out by measuring the old door height, and divided by 3 so I would have equal pieces. I made the new door 1 inch longer on the top and bottom on purpose so I could custom trim later. I made rabbett cuts to the panels where they meet so that they're water tight. I then laid all 3 pieces on a table, joined together as if they were in place in the companionway. I traced the angle of the sides using the old door, leaving the top and bottom extend a little more than needed. I then put the bottom panel in place and measured to get a good fit, then trimmed it at a slight bevel. Then I put the other two parts in the doorway and closed the sliding hatch cover until it touched the top of the new door. From the inside, I drew a line where the cover touched the door. I then trimmed it with the saw, and sanded all of the edges for a smooth finish. I then painted it with rustoleum, using a color to match my mainsail cover. I expect it to last for a long time.