well i can tell you what works for me
3 or 4 coats of used motor oil.
Hyd oil works just as well.
learned that one from some old farmers. They used it to protect the wood post's that held the barbed wire.
I guess you could use new motor oil but that would cost you.
Used is free.
It can get a little slick but nothing soak's in and waterproof's the wood better.
Most of your best deck sealers and wood paints are oil based.
I dont need UV protection and i dont need color[pigment]
So that just leaves the oil.