The reputable RV parks that do allow short term rentals, charge a management fee to manage the site since it is assumed you (the owner) are not going to be there very often.

Some even charge for renewing leases. 

I think your estimates on what to charge for rent in Hastings is low.

@Christian Beebe You're saying you spend $150k on average per year with credit cards for expenses on income properties and you're able to pay-off on average 95% of the card balances each month leaving 5% exposed to being charged interest each month

The closer to 20% equity you are, the cheaper PMI will be, regardless of which option you take.

I would not take that owner financing if possible, I don't know about your market but that interest rate is double a good cap rate in CA and more than most hard money lenders would charge. 

I was looking at gas and water paid by landlord and thought I could charge $55 each for gas and water as flat every month fee.

In addition, the PM charges their "new tenant fee" equivalent to one month of rent ($1000). 

me and my sweetheart have enough for the down payment on a duplex. we want to save to install a granny in law suite in the attic. just a studio unless the numbers make sense for more of course. from what I researched it can run me 32k to 65k on the cheaper side if I can use unused space.our goal with it is to build the studio then live in the studio while househacking and renting the large units then when we save up for the next duplex do the sameAnd just rent out the studio for 5 600 after wardsturning the propertys into suido triplexes.any problems I may run Into trying to do this?

So if you put $100k in a savings account with them, they might be able to use that $100k as the basis to lend out $500k... and charge interest on it.