Grover:
This took some reading on my part. I agree with you..551.40 is for receptacles within the RV IMHO.
Again, 30-50 GF is not required. You may want to politely request the inspector to please re-read 551.
As to the 50 amp locations, yes they are required, BUT...your clients site may not comply with the NEC definition. See the wording '...vehicles of the general public'. IF the site is private....then you have no reason to comply with the 50 amp requirements, although you may choose to do so for convenience.
