In Oregon, for example, a land contract that's been defaulted upon can't simply be "yanked" and the occupant evicted, without  properly terminating the land contract; I've been told the procedure is similar to a normal foreclosure.

Any suggestions on where to get information to help estimate average annual occupancy? 

Occupancy is a huge issue with applying for coverage, so make sure you are upfront about your plans to avoid issues down the road.

In your purchase contract, you consider including a clause that allows the buyer and/or the buyer's agents to enter the property during the term of the agreement with reasonable notice to the occupants (if any).

Here are a couple more for you:MLS        multiple listing servicePA            purchase agreementBATVAI    buyer's agent to verify all informationCO           certificate of occupancy

The biggest factor here is occupancy.

On the low priced homes below 50k there is not financing for owner occupants so seller financing is the only option.

Establish an "unauthorized occupant" clause, with a hefty fee for violating this, in your lease/rental agreement.

Another thing we have done is do a low occupancy shorter term lease. 

Be respectful, open up a dialogue with any occupants.