Would you guys be concerned about this?

[Carmine]

As others have said, that's no concern.
For me, if you aren't going to drive the car on wet roads, I wouldn't do anything to it. That rust is stable.

Adding some 'proven' topcoat always has a mild chance of not performing properly.
For instance, it the topcoat is slightly porous and with not-ideal adhesion - it could trap moisture, which could create a bigger problem.

That's why oil base paint works well. It doesn't make some kind of hard shell barrier that can trap rust, but at the same time it's will give you years of extra life before scaling.

 

[sask67ragtop]

What I see in the images is that any rust under there is the result of road debris hitting the paint and pock-marking it, which later resulted in what is seen there. Clean things off, prime, repaint as necessary, and then some sort of undercoating to protect the paint in the future.

In the later 1980s, GM put an "impact coating" on the lower part of the bodies of their cars. It had kind of an uneven-smooth texture and was painted over with body colors. Unless you were looking for it, it was not noticed. Something like that could be good to use on the lower body.

Enjoy!
CBODY67

I had that coating put on my 67 Monaco when the body was done in the mid 1980’s to try and protect it from all the gravel roads travelling we had around home