I had a situation where underground oil tanks used for heating homes had leaked. One of the previous park owners had the old oil tanks removed, had the contaminated soil removed and registered the work with the state - and ultimately got a clean bill of health from the state. The phase one noted this and also provide me with a clean bill of health..
If you like the deal and can get the mess properly cleaned and signed off by the state (make sure the work is done by a certified professional, soil samples are done to confirm that it's clean, etc) I don't see a reason why you shouldn't move forward. If your park uses a well for its water source I'd think twice about moving forward however.