whats the market like for similar units.. that will tell you if your rent amount will hold up.Owners typically pay heat , water, sewer, trash in most multi family buildings and this is part of the formula in factoring the rent.  

I have been using wrong formulas for years.  

What formulas would a mobile home park appraiser use and what would say a bank or lender use also to access the risk?

This formula can also work with other forms of marketing, just switch conversion rate for what you using.Remeber to not stop, keep optimizing and testing.

Yet, when doing property evaluations and analysis, I've yet to see these fees being called out in the various formulas I've been shown (including the BP calculators).

@Avery Carl and my towel formula is as follows. 

After running all kinds of numbers from multifamily for sale, I have come up with the best scientific formula of all time and for you and for you only, I’ll give it a way for free.K.I.S.S it.  

Bonus depreciation is great, but when you combine that with great investment properties that produce cash flow and appreciation, that will be the best formula. 

Then the offer, do you work on the 70% rule or is there some other formula?

The formula being: Profit = ARV - Purchase Price - Rehab Cost.The problem I have is getting reliable figures for 2 and 3 — Rehab Price and ARV.For rehab price: getting a contractor to give me a ballpark estimate seems the natural approach, but that seems doable only for 1-2 properties.