Sikkens marine varnish
Start with Sikkens Cetol Mrine as a base over good sanded wood. Should need maybe three coats, then finish that with Cetol Marine Gloss. Once you do that you just do light sanding on spots and recoat with gloss to touch it up as needed. Depnds on how much UV you get where you live as far as how long it lasts.
If you keep up with it as spots develop and don''t let it get carried away it''s about as easy a finish as there is to maintain with the least amount of effort.