It sounds like you have a residential broker who happens to have a park listing.
When this happens to me, I write up a letter stating that I'm pre-approved for financing or with whatever else it needs to have in it. I send it over to my banker. He reviews it to ensure he's comfortable with it, transfers it to the bank's letter head, signs it and sends a separate email to the broker. I've never had a problem with a broker after I started handling those special whacko's that way. I use my local banker even for properties I know the bank would never finance.
Again, their financing is contingent on the property fitting into their loan portfolio. As far as me as a buyer, yeah, I'm pre-qualified by them to buy properties that size. So, of course I'm pre-approved. The property being pre-approaved is a different story.