The RMC needs "service bonding" on one end, which is something besides a regular locknut, 250.92(B). A bonding locknut could be used if there are no Concentrics.
So if there are concentric then I need to use a bonding bushing?
correct
No you can use a bonding locknut or bonding wedge. Whatever you use it's only required on one end of the raceway. I install them on the panel side in case the meter is locked so it can be seen during an inspection.
You will need a bonding bushing or a fitting that does the same thing on any metallic raceway that is part of the "service" which (in simplified terms) would be anything between the meter and the first disconnect. After the first disconnect, it becomes a "feeder" and you can bond the metal raceways with only the locknuts.
If you stay PVC all the way, and it is truly a service and not a feeder, then yes. If it's a feeder, you wouldn't need a bonding bushing anyway.
Yes you can use PVC for the portion below the meter. The metallic riser above the meter requires the additional bonding but that is accomplished by the threaded hub at the top of the meter.
