That looks amazing, good job.

Yes, I cut the end of a tool I would never use and formed a concave tip. I did have to back my air pressure down as the air hammer I was using was to aggressive. I have watched guys doing aircraft work with aluminum rivets where they use masking tape on the tip of air hammer to protect the rivet heads from marks. I did not go to that extent and still had good success. I did bolt everything together with 1/4 inch bolts and used C clamps if I had doubts about a tight fit. I have a couple of seat boxes I have bolted together that will soon meet the rivet process.

Looks excellent. We were taught to use a long stroke air hammer, reduce PSI, sometimes a dab of tape to protect the head. On grain trailers, there are many rivets. Many local manufacturers still rivet by hand, one rivet at a time. Tedious job to say the least. If any rivet head has a "smiley" face from the bucking head, it is supposed to be removed, for sake of professionalism.
When touring a facility, if we ever saw a finished trailer with an ugly rivet head, we walked away. Imagine waking up and bucking rivets daily! Not for me! Thanks for the photos. JM