"As river flow in spring time, so shall many shaving flow from pvc coated pipe."
I've threaded much of the dreaded pvc coated rmc. You need to buy the proper threading dies if you are using a "port-a-pony". It is a little harder to get the threads started, but you'll get used to it. Over all, it isn't much more difficult to thread than regular rmc. Make sure that you buy some pads, lead, or something to put between the conduit and the "teeth" of the vise, or the teeth of the "power threader" (if that is what you are going to use to thread with) so the the pvc coating doesn't get damaged. If you do damage it, you need to get some of the liquid pvc that is used to repair it. It comes in a can just like pvc cement that is used to glue pvc conduit. Even the straps, payne hangers, unistrut, ect should be pvc coated.
Man, you're gonna have fun on this job.
"As the squealing of a stuck swine; so shall be the voice of the "green aprentice" who humpeth the 4" pvc rigid."
In the spirit of Grasshopper,