The figure in the Chief instructions show the way of mounting I was asking about. In the figure they it as toe-nailed between the joists. I ended up running the base board across the joists.
I tried several configurations with the SBLU (bracket) that came with the RPAUW. It was a bit challenging because of the small size of the HD65. The three bracket holes were only about 4 inches apart. I ended up settling with this configuration for the bracket.
After measuring the proper location for the extension pipe, I ran a coathanger up into the attic space above to ensure there was clearance above the spot I planned to mount it.
This shows the attic space above. You can see the coathanger poking up through the ceiling. I was worried about the joist that runs down the middle of the room but after checking it, I knew the base I was planning to use would clear the middle joist.
This is the board I used as a base to run across the joists. I used a 1.5 inch floor flange to connect the extension pipe.
I cut out a hole in the board so I can run an HDMI through it to the rack.
I painted the 12 inch nipple with white gloss spray paint to match the RPAUW. I know, I know...what's up with the white? I have to maintain the existing color scheme for now.
I put the flashlight over the hole in the attic and it made it easier to trace out the hole to cut in the drywall.
I used the cap that came with the RPAUW to trace out the hole I cut. The little beam of light made it easier to center it.
I didn't have a large hole bit for my drill so I cut several smaller holes and used a blade to cut it out.
It worked out pretty well. The extension pipe fit tightly.
There were M3 screws of two lengths included with the RPAUW. Unfortunately one was too long and the over too short. So I got a size between the two at the hardware store.
The bracket attached.
The RPAUW attached to the extension pipe.
Finally got it up. Next up, order the HDMI cable and run it through the attic to the rack area.