It's kind of hard to see here, but I drilled out four rivets on each side where the bottom skin attaches to the flange of the outboard most seat rib. The flange of my doubler is going to lay over this flange and the whole shebang will get riveted together.

Kerin helped me hold the flange of the doubler down while I drilled up through the existing holes with my hinge bit.

These little spacers are made of .040 aluminum and will go between the joggled flange of the antenna doubler and the flange of the rib. I need these spacers because that rib is joggled and otherwise the joggles would inhibit a good, tight riveted joint.

Got 'em match drilled to the joggled flanges of the doublers.

The back side of each spacer needed countersunk. I clamped a couple scrap strips of .040 to this block to prevent the spacers from spinning while countersinking them. Worked great!

All spacers countersunk and deburred. I'm probably not going to prime the edges of these.

The bottom skin needed dimpled, but I had a heck of a time trying to find my 3/32 pop rivet dimple dies. They finally turned up in a toolbox drawer they shouldn't have been in.

I've only used these once or twice before, so I didn't recall if they would do a good job or not. I was pleasantly surprised to find out that the dimples came out great on this .025 thick bottom skin.

I also dimpled the rivet holes for the doublers. I'm undecided whether to prime these or not. On one hand, I think it'd be good from a corrosion standpoint to have at least the bottom side of these doublers primed, but on the other hand, I need to make sure the antenna makes good contact with the ground plane.

Towards the end of the evening, I started making doublers for the transponder and ADS-B antennas. Since these antennas are much smaller, the doublers won't be riveted to anything. Instead they'll just be sandwiched to the skin with the attachment nuts. I cut them out of leftover .040 almuminum from when I redid the aft deck.

Got 'em deburred and drilled except for the BNC connector hole. Tomorrow I'll try to decide where to place these. Don at Delta Pop indicated these need to be at least 60 inches apart since the transponder is pretty high power and the ADS-B antenna operates at nearly the same frequency (1080 Mhz vs. 978 Mhz).