I would use pipe in your case just to be safer and to make sure everything is in place. I also had this problem, and because we wanted to match our roof-decking with the garden design, we had to re-roof. Our designers and workers advised us to use pipe as well as it's really resistant and we did it. I don't have any problems with it now and everything looks great. I hope you also found your solution to this problem and if you did, what did you use in the end?