I had always thought, primer shmimer. I painted a bottom board with two coats of paint, no primer. Figured that was for people who liked extra work. In a short time, about a year, it was pealing. Someone said a primer provides a stickiness between the wood and the primer. Goes along with what Ed just said.
So that means painting with primer, waiting. Painting first coat, waiting. Painting second coat, waiting. And no access to cheap exterior paint, and hating just the thought of painting.....
I have used, I think it was, Teak oil I saw recommended for bee boxes. I thought it went on with a rag easier than the paint. I applied two coats and it looked good the first rain. But I'm not sure there's a difference from the untreated ones a few years later.
I have been thinking of collecting propolis and mixing it with turpentine to apply.