I finished the pedal access door today. First, I riveted the rest of the platenuts to the attachment ring, then re-primed the "outside" surface of the ring. Next, I dimpled the fuselage skin holes, then riveted the ring to the skin. Finally, I screwed the cover plate on.
I see one small place where I'll have to file the edge of the cover plate a tiny bit to maintain a perfect seam width, but other than that, the cover fits very well.
I know this was a relatively simple modification among all the others I've done (and will do), but I'm especially pleased with the way this one came out.