I have one park and my Dad has three in Washington State. If our leases are correct and properly recorded with sound park rules we have never had any issues whatsoever. Washington State is very, very liberal and supportive of affordable housing. There is a very strong MHP Association that works diligently to protect park owners and is very active in State legislature.
The State also has a Tenants Union that assists tenants and landlords with individual disputes. The very closely follow and adhere to the Washington State Landlord/Tenant Act that is very clear and easy to follow. Fortunately or unfortunately the Tenants Union is very very overwhelmed and usually does not respond very promptly whatsoever to any individual requests for help. If you Google up the Wa State Landlord Tenant Act you will see that is neither pro tenant or pro landlord... it is mostly pro leases/rules and communication. (my opinion).
One thing that my father did dig up last year was that Washington State allows park owners to place any age mobile home or RV into their parks as long as they are not pre hud. Individual Cities and towns cannot set age limits anymore. Home has to be primary residence and indoor toilet.
Lastly- all our parks are in Eastern Washington. We prefer the smaller less regulated counties on the rural side of the mountains. Western Washington particularly King County is much much more regulated. Permitting, land use, building, site improvements etc are much much more regulated and controlled.
Congratulations on your park and I hope it goes well. If you have any other questions about Washington State just let me know. I own parks on the side and have a day job on the other side. Lived my entire life in Washington. Beautiful part of the country.