I would value it at 17 lots collecting $350/month and determine a reasonable value for the 6 POHs based on what they can be quickly sold for. With POHs rented at only $100 above lot rent they are losing money every month. It is important that the cost of maintain these POHs be deducted from your monthly income in calculating the over all value of the park.
Determine a cap rate that will make the purchase profitable based on a adjusted income and anticipate lowering the value somewhat to allow for deferred maintenance.
I agree with Greg with one exception. After you determine what the 6 POH’s can be sold for subtract 25% or so. You deserve to make a few dollars selling them.