I had the lower hinge screws on the door to my 22 come loose a couple of years ago. At first I figured I would just through-bolt them, but as it turns out it's not quite that simple as (at least on my 22) where the fasteners would come into the cabin would just happen to land on a totally un-flat molded/ridged area. So I would have had to do a fair bit of modding to make a place for the washers/nuts to land. Hence I decided to tackle it a different way.
What I did was to remove the hinge, and overdrill slightly (but not so much it would show beyond the hinge), dig a bit of core out, refill with neat then thickened epoxy, and then put the screw in while the epoxy was still soft (green stage). I may have waxed the screw for future removal, but I can't remember at the moment. Another way to remove (so I might have done this instead) is to just put the screw in to the green epoxy, and then if you need to remove it later on, just touch something like the tip of a soldering iron to the screw head -- the resulting heat with soften the epoxy enough so you can remove the screw. Thinking about it, I probably did the latter so as to give the screw the best grip.
I also bedded the hinge with a bit of butyl.
Has been sturdy ever since then.
Sunbeam
PS: The core wasn't wet at all, but just that balsa doesn't really give much grip to a pointy screw, and the hinges C-Dory used are kind of "cabinet hinges" that get some strain on them if you open the door fully. So between those two things, it wasn't surprising the screws let go.