I'm not sure what you expect the RV park to do they aren't going to be watching your RV 24/7. Essentially when you left it was like being in storage while you were gone for a long period of time. Just like when mine is in storage right now and the storage owner isn't responsible for damage that goes on there. But my insurance is and I don't understand why you have allowed your insurance to get away with not covering your damage. You don't have to be present and witness who backed into it just that it happened and now you want your coverage that you are paying for. If my insurance didn't cover repairs for whatever reason I would tell them meet me in court.
Just my 2cs.