I think the sewer line issue will depend on the State you are in and the mobile home laws of that state. I am very familiar with 2 States (not NJ) and laws in those 2 states say that any water and sewer piping underground belongs to the park owner and the piping above ground belongs to the home owner. Each is responsible for maintaining/replacing their own. I would bet that NJ is the same, but it's something you'd have to check on to be sure.
On the parking pad....the same advice goes...check to see if the law covers it. In the places I'm familiar with the park owner has to furnish a parking spot, but they are not clear on what the condition of the spot has to be. In other words if there is a place to park a car the park owner might be meeting his obligation regarless of its spot's condition. Check on what your State law says. There should be a separate set of laws just for mobile home parks. Try to find a MH Renters group. They will come up with the laws for you.