The home rental income should not count towards the value of the Park.
If there is a trailer worth 5K that brings in a $200 lot rent and $300 home rent then this home brings in $3600 per year in revenue for the home rent component, minus 40% expenses is $2,160. At a 10 CAP that's $21,600, which is a significantly overvalued home. This is why banks that lend on these a lot don't give home rent value as part of their appraisals.
Your valuation should be based on the lot rents the Park generates + the sellable value of the homes. If they are a bunch of 80's and 90's homes then probably between 3-6K each. Inspect each and assign them a value based on repairs required and value when ready to sell.
F&D use a quick formula for valuing a Park on the fly - it's Lot Rent x Pads x Multiplier. The multiplier should reflect the expected expense ratio. If it's a large Park that you expect a 30'ish expense ratio then a 70 multiplier would be merited. Adjust it down for small Parks, Private utilities, or other recurring expenses that impact profitability. So a 20 Pad Park pulling $200 Lot rent with near a 40% expense ratio would be worth around 240K at a 12 CAP. Do a detailed analysis once you have their rent rolls and tax statements.