So much much hotter than 212F too? My fin jig is the plastic Estes one, which probably also would begin to deform if I reached the right temperature. Maybe I can come up with some metal method, blocks in a vice where I could at least heat/fix 2 opposite fins at a time.

My heat gun does a nice job of softening, deforming and melting PVC pipe, which is of course much thicker. It's just a challenge to stop short of real damage.