I had this happen during diligence on a Park outside Kansas City too. Was able to get an e-mail from the Zoning Manager confirming the property was non-conforming and no issues moving homes in and out of the Park. This was a small town and they don't issue Certificates of Zoning. My plan was to have it notarized and filed with the County Clerk, along with the zoning map, zoning ordinances, etc. But the Park was a pile of crap and seller wouldn't negotiate so stepped away.
It seems like the best answer when formal certificates aren't issued is to just talk to everyone with the city, county, MHA, etc. to get comfortable and get as much documentation as you can so that if it ever comes up you have a good case.