[Bennett548]

If you are sure you won't be taking it apart, look into structural adhesives. The area between a gusset plate and tube is pretty big and thin, so an epoxy or CA glue can add a lot of strength. We love Black Max (Loctite 380) because it doesn't get brittle so it can survive impacts and shock loads. Be prepared, it is extremely messy.

I would suggest self-drilling, self tapping screws to hold everything together while the glue or epoxy cures, and to add a little strength.