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once ospho is applied,repairs are done and painted, i would spray oil inside of frame rails to prevent rust.



A twist on this is a process used on rust prone Jag box section chassis. Use a rust proofing gun (multi-directional nozzle about the diameter of a pencil on the end of a plastic tube several feet long) and saturate the inside of the rails with penetrating oil. Let it drain then repeat with waxy rust proofing like Eastwood's product through the same gun. Best done after repair and painting with plenty of junk drop cloths. If you're able to get the rust cut out before capping this process should give you a durable weather resistant chassis.