I found with a heat gun I can get the heat where I want it and control the bend better. If the whole thing is a noodle then you are fighting noodles! Electricians have electric ovens designed for this that clamp over the pipe, right in the middle of a 20' length if that's what you got. With the heat gun though, as you fit it to your template you can let it cool in the place that's bending too much, and heat up the place that isn't.