I've used this stuff before and it worked good for me. Used this as the primer on a 85 Ranger that I brought from Minnesota and then Painted the floorboards over it.
http://store.interstateproducts.com/rust_converter.htm?gclid=CISp0PP30YwCFQi9VAodMRJttQ
http://store.interstateproducts.com/rust_converter.htm?gclid=CISp0PP30YwCFQi9VAodMRJttQ