Sorry for not responding earlier.
So you are saying that there are 28 lots @ 250 per month giving annual gross revenue of 84,000.
On a (640k minus the down) 480k loan , 25% down , 20 year ammo 7 year ballon , (I'm using 5.5% because i did not see a rate posted) looks like your monthly payment on that is 3301.86. .
Working backwards, you need NOI of 4952.75 to achieve a 1.5 DSCR as you are stating the local lender would need to underwrite. That translates to annual NOI of 59424. Equating a hypothetical property operating expense ratio of 70%. With a park with this vacancy ( not as many occupied lots to spread the fixed costs around) and water leaks. What are the current expenses showing at?
You say the deal is pulling strong test ad demand which is a good sigh. If there is rent upside , you get the guy to budge on price, maybe find a lender who will stretch the ammo to 25 , and find someone who will also do a slightly lower dscr, there could be something here. This will all hinge on getting into the higher expenses and seeing what the root issue is and see what the resolution will be (also in terms of capital needed for the fix).
If you want some help to look over the specifics i can take a look or if you pass on it , I think it worth prodding into a bit more.