Those are pretty restrictive CG policies. Usually if canceling this far in advance the CG will allow full refund, as they fully expect to rent the site. Or at least will charge a deposit fee.
However, if they informed you of those policies when you make the reservation, you have no recourse with them. But you have nothing to lose by pleading your case with the owner. Try that. Otherwise just eat the expense and use the credit later in the year.
My Open Range gave me nothing but problems since the day I bought it. A real POS from day one. Back to the factory for repairs, and they fixed all that needed repairing. But new problems kept cropping up. Then it got worse.
Finally got rid of it when the payoff crossed below the value.
There are just some real bad trailers out there. Sounds like you got one. Trade it if you can.