Like all good learning experiences, my tanks leaked; both of them, mainly from the rear seam.
The one tank leaked from the seam near the fuel sender and access hole. This was easy enough to fix by removing the access panel and adding more goop.
The tank in the picture leaked from the top seam near the middle, in 2 places. Ugh.
There were many options I found on-line to fix this:
1) use Loctite adhesive designed for just such a repair.
2) ignore it and hope it goes away.
3) cut a hole in the baffle, add more sealant and then use a new access plate to cover over hole.
4) use the really thin Proseal that is brushable, pour it in the tank and slosh it along the seam.
5) make a funky applicator with a syringe and tubing; using a USB camera, and add some more Proseal to the seam thru the filler neck or the sender access panel.
Of course, being the expert builder that I am, I did none of the above.
I decided to use option 6), which is not listed above. If that didn't work, use option 3.
Option 6) was to drill out the baffle rivets in the offending area, wrap a towel around the vacuum cleaner nozzle and tape it to the fuel filler spout. With the manometer hooked up, turn on the suction and leave the fuel sender screws out to avoid over pressurizing the tank (wouldn't this be under pressurizing?). Add some Proseal to the seam, and gently open the seam up by gently flexing the tank skin. To my surprise, the sealant sucked itself into the gap. I used a heat gun to gently heat the tank skin to help the Proseal flow into the cracks. The whole time the tank was under 27" of vacuum.
After resetting the rivets, I let the tank sit for a day. I started the pressure test tonight, and the leak check using soap bubbles showed no leakage. Normally I would say done, but I plan to let it sit over night just to make sure.