Personally I don’t think you can chase down rust unless you do as the classic car guys do and take panels off( I don’t mean unbolt panels . I mean welds and spot welds). Cars and trucks rust from the inside out.
If I was in your shoes I would look to dig out the worst, seal up and paint. Treating internally can give it more time with the likes of fisholene or lanolin. I have just spent 50k on a body resto on a 70’s Holden and it’s a bottomless pit if you want to do it right. Just my thoughts.
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