Someone gave me the measurement of 31.52 as the outer diameter so we did 31.90 and it was still too tight so you may want to expand it a bit. I sanded the inner diameter of the first mold to make it fit without fearing I was going to break the camera gimbal. Good luck and please give me a link to the flexible material is definitely be interested in a softer alternative.
Thanks Steezy...the material I am referring to is ninja flex and can be found here http://www.ninjaflex3d.com
I use the ninja semiflex for cellphone covers and it works great just print like ABS with a bed temp of 65c and a extruded temp of 240c that is what has been working for me after some trial and error...