Not sure about most Mfg's, but my gas lines are black pipe which eventually rust with exposure. Not sure I've seen cast iron in any applications.
Either way, I think it would take decades to compromise the black pipe or any iron type pipe for that matter, however, a simple process to protect surely can't hurt.
I've only seen Scothguard green gas pipe for underground residential, never for RV's, due to its higher costs.
Bob and Better Half
2007 F-250 PSD, SW, CC, LB, 2WD
2006 TF32SS Cross Terrain Toy Hauler (sold)
Reese 16k slider