The only things that really jump out at me is that half the income is from trailer rentals. That's OK, but if you are getting financing for this, the lender will value the lot rental differently than the trailer rental. One is real property, the other is chattel.
So you might find that the lender is only willing to lend based on the income derived from the real property. But each lender is different, etc etc.
As a result, I would look long and hard at how much you are paying for the park and how much you are paying for the trailers. The trailers should be pretty cheap.
The other thing that struck me was the manager living there for free. Typically that's a terrible idea. Even if the math works out the same, paying the manager a salary/commission/whatever and then being a regular tenant avoids confusion in the manager's mind over his proper role. Nothing in the park is his. He's a tenant who happens to have a job located very nearby.
Other than that, there's the usual due diligence stuff. Inspecting everything, making sure things work, testing soil, etc.
On the face of it, seems like an OK deal.