Rust proofing runs about 120$ up here, company called Krown. Not sure if you guys have this company in the states but if its done regularly then it should help against it.
They spray the crap out of your vehicle, inside the panels... I mean everywhere. I did that for my old Mazda pickup and it helps. The PO had done it, I could see traces of it on the inner portions of the jeep. Was also undercoated by the PO. I may do it next year or every other year to keep the routing going.