There is a product called POR15 that really works great. A lot of the BMW 2002 restorers use it. It simply is painted over rust and stops it dead.
It aint cheap, about $35.00 a qt. but it works and you don't have to completely remove the rusted metal. I used it on my son's old BMW trunk and it is amazing. I think I posted about it (POR15) 4 or 5 months ago. If you cant find it, look at
www.firstfives.com.