The exception should be made but HOA's are run by people. In this case it seems the people are being unreasonable.
Those who say they would not live in a HOA neighborhood like myself could still have an issue with an occupied RV being parked in the driveway.
In many communities it is a violation of zoning laws to have an occupied RV or 2 residences on the same property. The zoning board would have to make an exception or look the other way. Seems that making an exception would be the simple thing to do , but a zoning board could easily deny the request just like the HOA.