The rest of the rudder parts had more work ahead before they could be primed, but the stiffeners and skins were ready to go.
Since I'll be able to backrivet the stiffeners to the skin well before assembling the rest of the rudder, and since it was a good day to do some priming, I went ahead and primed them. It took a long time to prepare and finally spray the parts so I didn't have much opportunity to take pictures along the way.