64 valiant floor pan rust, practical fix?

If it were me I would sand and spray with rust reformer . The most important thing is to do the same underneath . I personally might just use some fiber reinforced bondo and apply to the inside making sure to do a big enough area where you are covering any compromised metal on the one with damage. ( check others for compromised metal ) I'd then spray a little primer and paint inside and out and spray some undercoat under there to keep the area from getting any more damage.

Should be about a 10 dollar fix if you have some supplies, a bit more if you don't . Don't make it a bigger deal than you have to . I'm sure evryone on here will agree with me. :)