I agree wholeheartedly. Do Not use polyester, which is fine for laminates upon itself, but does not soak into wood anywhere like Epoxy
. Dilute the first coat as recommended. Over here in Australia, all exterior ply uses "A" bond glues, the same as marine ply. The difference lies in the heartwood plys, which in exterior can have knots and small voids, whereas marine grade layers are all first grade.
I'm not a great fan of plywood rudders even if epoxy
coated, choosing solid timber instead because plywood sucks up water and breaks down much more quickly than solid. I'm thinking of a break in the sheathing, a nick, dent, whatever as time goes on. Oregon is frequently used diagonally laid, epoxy
glued and bolted.
Re your boom. Again a good quality enamel will be better. It's more flexible than polyester, easier to recoat, and does not break down so quickly with UV.
Or use a durable number one timber and let it go grey.
PS: My first rudder was polyester sheathed, which split and allowed toredo worms in. First I knew of it, my rudder seemed wishy-washy and when I dove to inspect, the whole damn thing was flopping about on its fixings!