I don't know about these parts, are they pop riveted? In that case there is a lot of crush force on the pithy inside of the tube, and you might have been as well off if there were a glass patch on the inside of the tube first, where possible. I did that on my fenders. Another option is hardware bonding. It consists of epoxying screws into little lakes of epoxy, where the epoxy spreads the load over a wide area. So you might drill a fine hole, then a larger one at least 2x shank, and more is better, and then fill it with appropriate epoxy. Use the tighter portion of the hole to snug the screw while the upper part contains the epoxy, This could be tough to do without 3/16 -1/4" in thickness.
Another thing with pops is that they leave a piece on the inside of the tube, That is OK so long as there is a way to shake it out. Another option is to let them fall into a narrow section and inject epoxy to hold the rattling piece.