You're kidding right? So you are going to report three hundred mobile homes purchased located at the same address over the course of a year (assuming this is a high volume dealer). Hopefully, the dealer is in a low income census tract - think of the CRA credit you are going to get.
Tell this auditor to go crawl back under the rock he has been hiding under for the last 15 years.
Since this a pretty wacko take on the regulation, you probably won't find it specifically addressed. I would suggest that you make a joint call to the HMDA Helpline and I am sure they can set him straight.