So, ultimately here is what I did: Built a dome form (two half-circles of plywood, notched so they would interlock at a 90-degree angle) Cut an arc from plywood as a bending form Heated PVC and bent it around the bending form. Once I had a complete circle I placed it on the dome form. Did this four times for 4 different circle diameters. Laid chicken wire over the circles and wired it in place. Watered down yellow glue + brown construction paper to papier mache the outer form. With the second layer, I sprayed expanding foam onto the existing layer first and smeared it out before laying the second layer pieces down (i did this in sections - the foam sets up too quickly otherwise). Once this cured, it make a surprisingly rigid shell! Build a base and stood the hemisphere on end, on the base, and screwed it down. Single layer papier mache on the inner surface, also smearing the paper with spray foam before attaching it (so it would bond to the wire). Came out great - not a perfectly smooth sphere, but that's kind-of expected with chickenwire.