Thanks so much for the tips Pete. I never would have thought to paint the boards and ends before construction! It looks like the consensus is white or light paint, preferably with UV protection and oil-based. Quick followup: You mention linseed oil. Could I first apply a coat (or two?) of linseed oil by itself, followed by the paint? Or is that overkill? I’ve been meaning to buy a canister of linseed oil anyhow, so the added cost is not a factor. Thanks again.
Probably overkill. If you add some to the primer don’t add much.You could hit the board ends 2x with the primer It should soak it up. If you use too much linseed oil It will take a long time to absorb/dry!