Depends on how committed you are.
A tube can be replaced. Than it needs a repaint.
Other way to go, I think, is cut away the rusty stuff. Preferably go the mechanical way. Only opt for chemical ways if you can't reach a spot. Get rid of all rust. Than braze a piece in place, covering the hole. Probably it needs a reapaint as well, if you want to do it properly.
Now give it a proper protection against rust. Use for example a spraycan FluidFilm AS-R ...and even Mike Sanders as 2nd a bit later if you have compressors, gun and waterboiler.
Personally I would go for the 1st method, the tube replacement. With the 2nd you still run the risk the ube will rust at another place, were it is also very rusty. The converter doesn't really kill all rust. Have more faith in proper oils and greases, but you never know. Moreover tube replacement looks way nicer also. When done properly of course.
A Few Years Ago,i Say Afew Its About 8 My Monster Became Porus At The Bottom Of The Seat Tube,because Of The Lack Of A Drain Hole, I Had It Repaired But Its Back.a Tiny Little Rust Patch About The Size Of The End Of A Pencil Has Appeared With Water Uzzing Out. This Is My Question , Do I Repair It Again With A New Tube Fitting A Hole This Time Or Rub Down The Area ,use Some Rust Kill And Tig Weld A Fancy Looking Plate Over The Hole,.i Can Only Then Respray When Monster Decals Are Created.what Doya Think