Take it as a learning experience especially if you are getting started. Your time will be well spent looking at it and make you a better investor should you decide to get into parks. The park in itself with vacancy is not a deterrent. When you say that a lot of parks in the area have vacancy , it can be more of a concern. My next step would be to look at who owns all the parks? Are any of them corporate owned and managed or all mom and pop? If its corporate thats more of a concern, if mom and mom , still a concern but maybe not as much.
Whats going on with the local economy/ general trend of people leaving, coming, sideways? Any projects in the works ? What are the lot rents of the park and the ones surrounding it, whats the unemployment rate, average house price, average 2 bedroom apartment rents according to best places.net?
You are buying the park and the market so you have to research both in depth. Here you will want to put a lot of additional emphasis on the market. Good luck