Expected expense ratio for park with lower rents?

Any idea how to adjust expected expense ratio for a park with lower rents?

Park has 53 occupied lots @ $175 a month.

Park has well water and commercial septic. City water is available on the property, but not used as the wells are working.

Roads are 65% owned by park and 35% owned by the county who maintains the main road all the way through the park.

Would we still assume a 40% expense ratio going in?

Commercial septic what do you mean by that? There is a huge variation in cost to operate septic and lagoons on the low end and package plants on the high end.

By commercial septic I meant larger tanks supporting multiplelots. It is not 1-2 lots per tank as I have seen.

There are I believe about 15 lots per septic tank.