Battery breather hose corrosion

My Mk1 has a small amount of corrosion in the boot floor where the battery breather hose exits the body.

The paint work is bubbling, having given it a firm press the metal seems sound.

How quickly will it advance? Should I leave it? Should I get it cut out? Will it cost much? Any advice is appreciated.

Treat and paint it.

Picture would be helpful👍

If it’s not holed apart from the breather hose hole then a wire brushing or flap wheel on a drill should deal with the rust. Scrape off any loose stuff first, you can then apply a rust converter, Halfords carry these types of product. You can then apply Hammerite or a suitable paint to finish. If your particular about looks then finish in a body colour matching paint.

Thanks for the steer. I’ll give it a go over the Christmas break