Unfortunately, there is not much you can do unless you can show that this tree was in such bad shape that the park should have removed it.  I suggest that you make a claim to your insurance carrier on the camper so as to make sure you get compensdated.  You can try hiring a lawyer to deal with the state on this issue, but i do not believe that you will get very far.  You can also try suing the state in small claims court for their failure to remove the rotting tree - this may get the reaction you want that will get the state to settle with you.  I suggest talking to a lawyer in your area to explain the whole story.  If the park just spent money to clear out all the trees and missed this one, there may be some liability if you can prove they knew or should have known this tree would be a hazard.  It is a up hill battle.