The advice to clean up your finances before doing this is well grounded.Lots of gurus promote real estate investing, especially wholesaling, as a quick and easy path to piles of cash. 

He’s cleans the common areas of the park like picks up litter, mowes the grass, etc. he lets me know if there are any violations.

I've never done it, but I wonder if a possibility in some situations is simply to tie up the property through a legal proceeding so that the seller can't sell it with clean title to anyone else for an extended period of time.

For one, this isn't a criminal matter and so the police will not get involved. 

I've seen some wholesalers say that they are consistently getting deals on the MLS- their method involves making LOTS of lowball offers.

Under that structure you would be regulated by the SEC and the whole deal should be structured accordingly.If you are planning on having some level of active involvement in the operations and not completely relying on someone (The GP in this case) to manage your capital with the expectation of future financial return on your invested capital then you can go ahead and just go the "partnership" route.

Unfortunately many giving advice on here also have no idea of the risk involved in renting to certain tenants and will give the wrong advice.  

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

I am unable to find a sample clean up letter so I'm looking for advice on how to write up a letter. 

The amount of money involved is so little that it needs to be flagrant and egregious for AG or anyone else to take action.If you are ticked off at your property manager, change property managers.