I just used a skate helmet ($20 on Amazon) for a pilot dome reinforcement. It should work just as well for a whole dome. People have also used hard hats for their helmet scratch builds.
On that note, you might want to use something better than hot glue. I recommend JB weld. Tack it together with hot glue in a couple key points and then use JB weld to hold it better, much like a professional welder uses a tack weld to hold the piece in its correct position and then runs a proper bead on the seam.