I'd poor the concrete a little higher than grade, embed some kind of anchor to the top of it, and then set the post on top of the footing rather than inside of it. To me, inside is asking for it to hold water and rot in time. on top, it stays dry, but if anything happens you can always replace it without disturbing your footing.
That is what I did for a trellis around my carport. I put threaded rod in the concrete and made anchors out some decently heavy angle iron I had. Eventually its gonna rot and as you say its easier to replace that way.
