I would try to stay away from any glue joint at all in water most will just become a week point. it looks like you drilled through and then carved out a slot for the L to fit. that seams like a good track. I would love to use teak or some other water and swell resistant wood. Hard wood would be better. then seal the whole thing in Epoxy. if you really want to get into it I would do stabilize it with an epoxy in a vacuum chamber to let it soak into the wood.