The RV park is not responsible for damage to your rig caused by the collision of another driver. It's no different than getting your car hit in the parking lot of a grocery store. The store is not responsible.
As for the damage from the vendor, you'd have to take it up with the vendor. Just because the RV park allows them to come into the park does not make the RV park responsible.
I'm not an attorney, and may be wrong. But you can certainly consult with an attorney to get a legal viewpoint. If they think you have a case, you can retain them to represent you.
What would I do? I'd evaluate my insurance coverage to make sure I'm covered in the future.