I typically send to two different addresses: the Registered Agent address as well as the Owner’s personal address.
You can obtain the Registered Agent address through a free title company search, or by looking up the owning LLC at the relevant Sec of State website.
You can then typically find the Articles of Organization for these LLCs, and this will give you the names of the members. You can then take these and use one of the various free people search services (Whitepages usually works) to get their personal residence address.
I don’t think much is accomplished by mailing the park directly, but would be curious to hear other opinions on the matter.