When I first tried a smaller piece of rubber I had the oven set at about 150deg c
and it was starting to smell like a burn out.
If you want to know when it burns I can take my infrared thermometer home from work and heat gun the rubber untill something happens and get you a proper temp.

The santoprene I was thinking of using is good for a constant 130 deg and short runs of 150 deg.
I should be speaking to a company that sells santoprene tomorrow if I finish work on time.
If i find out more I will post any new info.