I epoxy glued a bolt to the center of the under side of the panel.
On the tube I drilled a hole in the center to match the bolt.
Slid the bolt through the tube.
Put a washer and nylon lock nut on the inside and tightened away.
I had to use a very small socket wrench, and small turns. This way I can take it apart if needed.
The exact thing happened this past Hockey season. At an event we were trooping between periods on the Ice playing "broom ball" I went down on the detonator. Lots of pieces to re-assemble. With the nut and bolt idea I was able to put Humpty back together again just like new . Even with a new paint job.
I'm sure there are many ways to assemble but this worked for me a couple of times so far.