I honestly don't remember what schedule it was, only that it was the common (probably 2") stuff from Home Depot. My somewhat "alarmist mentality" probably came from another alarmist.
But yeah, I hear you on the engine compartment temps... doesn't really seem as though it would have gotten hot enough to affect the PVC.
I may give this guy's intake design another look. It certainly would flow smoother than my gutted stock intake tube.