Here's what we have, as my partner is about to walk a park with an owner....to get more info to put in a realistic offer:

1. Lot number
2. Year manufactured
3. Roof style
4. DOT number
5. Condition 
6. Ownership
7. Occupied/vacant
8. Current lot rent
9. Wholesale value
10. # bedroom and bathrooms
11. either square footage or dimensions (I don't know what the standard is here)

Any other important information regarding existing trailers?  This is a 28 lot park, the owner owns 26 of the trailers.

You probably already know this but it’s not listed here so I’ll mention it.

On any trailers that are occupied, get an estoppel letter from the resident to verify what they are paying and what their lease terms are

My suggestions:

12.  Do the homes have skirting?  If yes, what condition?

13.  Is the hitch still attached to the home?

14.  Interior condition (if you can enter the vacant homes): check floors and ceilings for signs of water damage.  Check kitchen and bathroom condition.

What does it mean if the hitch is attached to the home or not? Does this have to do with them being able to move the home?