These photos show the priocess I used, however I got the size wrong, so I ended up doing the whole process three more times before I got it right. So all these photos show an under sized strap, but the process is the same.
I traced the shape on to some MDF
Like I did on an earlier piece, I used strips of self adhesive weather strip for the ribbed pieces
Then I cut a stack of 6 MDF end tags
Then I glued them in to place and boxed it up
A coat of petroleum jelly to stop the silicone weather strip from adhering to the casting silicone
Some Ultracal 30
Latex poured in.
A spray of Plasti-Dip and they are done! Then I just had to go back and make them the right size, but the photos show the process anyway.