Expense ratio on smaller parks

I am looking at buying a park very near my house that is only 20 lots.

I don’t trust the sellers numbers and will be rolling my own estimates.

I have heard that most expenses on a park are in the 30-40% range. Can I use this estimate on a smaller park such as this?

Park Setup:

Currently users pay for electricity and gas, but the park provides water. The first thing I would do is sub meter the water.

There is 1 small park owned asphalt road in good condition.

19 homes on 20 pads.

Would 40% be a safe expense ratio to use? IE 19 lots x $160 x 12 months x .6 / .12 cap rate = $182K