[abn]

Like Hal said there are as many answers to this as there are people...If you can not sand blast the area and it is "surface" rust then I would sand and wire brush away the loose rust, use a commercial rust converter like Ras-O-Nil available from Len at www.autobodystore.com (I have used it with excellent results), then coat the area with Corroless or your favorite rust resistant coating (a bit of my undecarriage was red oxide primer so the corroless didn't stand out that much.).