Step 6: Add another nut (or other support)
Three key points:
1. Put the nut most of the way onto the bolt, then add a bit of glue and back the bolt up to bring the nut/glue to touch the plastic. This way the threading will match for both nuts.
2. Once again, be careful to use as little glue as necessary for a good bond, and avoid getting any on the the threads of the bolt or nut.
3. Back the bolt up only enough to touch glue to plastic. If you "squeeze" it onto the plastic, the threading of the two nuts may be slightly mismatched and make it more difficult to turn the bolt.
Note that an actual nut is not necessary since there is already threading on the first nut. If you can find a washer with the perfect-sized hole to fit the bolt, that would work as well, and maybe even be preferable, because variations in the bolt threading could result in a mismatch of threading between two bolts spaced an inch apart. One option: drill into the second nut with a drill bit just thick enough to eliminate the threading.
That said, I used two threaded nuts on mine and have had no problems.