It is not unusual for additional buildings to be included with the mobile home park. Usually these are structures such as barns or sheds for equipment used around the park, self-storage, a clubhouse or houses and apartments.
Barns and Sheds - not much to say here; they are utilitarian, and typically not a big value add to the property, often used for storage of equipment to serve the park.
Self-Storage - can be useful for park residents, giving them additional place to keep belongings, resulting in a neater park with fewer items stored on lawns or driveways. Rental rates will typically be lower than self-storage at a standalone facility in the same market due in part to the stigma others may have of mobile homes parks, resulting in lower demand.
Houses and Apartments - finding a modest single-family home on park property which previously served as the owner’s residence is not uncommon. These of course have value, though not often as much as the sellers may think. Like self-storage, these will typically rent or sell for a little below market value due to their proximity to a mobile home park. It is also important to find out the parceling situation for the house or houses; are they on the same parcel of land as the rest of the park or already parceled separately? Subdividing and selling is one option; take into account cost, if it is permitted in your area (there may be restrictions on size or acreage of lots which can be subdivided). Additionally, utilities for the house may be included on the park system, so providing an additional well or septic for the house may be necessary if considering subdividing. For example, one property reviewed contained a single-family home already on a separate parcel from the mobile home park (all owned by the same owner), but used the well that also served the park. While this set-up served the current owner fine, to subdivide would require a new well drilled to serve the single-family home exclusively.
Clubhouse - these were a popular common place and gathering area for mobile home parks in years past. Think of a pavilion or closed structure used for social gatherings available only to park residents. Many of these are currently shut down or in disrepair due to neglect. These may have some value or other purpose (storage for materials) depending on their condition.
To review, it is not unusual for additional structures to be included with a mobile home park. Always assume their rent or sale value to be less than market value due to their proximity to a mobile home park, be willing to explore options of subdividing as well as the demands within your market.