65d will warp in heat. Use 300. It’s plenty durable for its intended use, which hopefully isn’t dropping on the ground >_>
For mass production casting from a silicone mold, SmoothCast 300 roto cast is the industry standard.
(Flex is not a huge difference from 300’s 70D by itself. )
Maybe I'm completely blind, but where is the application form at? I can't seem to be able to find it.
Edit: Nevermind I'm dumb and found it. I was looking for "Forms" and it's under "Requests". Might want to consider changing the wording in the first post to make it a little clearer?