This is how I did it. I'm pretty happy with the results, but still I'd be interested in alternate methods.
Cut three or four rings of 3mm EVA
Cut a wedge out of each ring
Glue cut ends to form truncated cones
Stack and glue
Round edges and scallop the rim
Glue base to stack: 3mm EVA with clasp pins
Glue central peak (5mm EVA)
Spray exterior with paint or Plasti-Dip for more-uniform appearance
Seal interior with PVA (Mod Podge, Elmer's)
Prime interior
Paint interior
When I find my heat gun, I'll try curling the edge on the next one. For now, this will do.
Cut three or four rings of 3mm EVA
Cut a wedge out of each ring
Glue cut ends to form truncated cones
Stack and glue
Round edges and scallop the rim
Glue base to stack: 3mm EVA with clasp pins
Glue central peak (5mm EVA)
Spray exterior with paint or Plasti-Dip for more-uniform appearance
Seal interior with PVA (Mod Podge, Elmer's)
Prime interior
Paint interior
When I find my heat gun, I'll try curling the edge on the next one. For now, this will do.