64 valiant floor pan rust, practical fix?

OP lives near the ocean, that "not so bad" now could turn totally blowed out and into a complete floor replacement rather quickly.

a picture is worth 1000 words, but when looking at rust it only tells half the story.

wire wheel that mess all down and it may be a beast of a different nature.
Salt probably wouldn't be as much of a concern as it would be driving on a lot of winter roads. I'd be careful not to create a situation where metal replacement is the only option .