Rust will never go away,the only way to fly is cutting it out and welding in new panels,been there and tried the glass.................it is a band aid at best !

fiberglassing a floor is by far the easiest solution, however, it will not add anything to your restoration value! In order to bring a cars value up you should always have professional patch panels welded in. It all depends on what you want to do with the car? Do you want to drive and enjoy it or restore it to enjoy but with an end result of someday selling it?