If it gives you piece of mind, I'd use the frame saver. I've never used it on any of my bikes...but I don't live near the ocean.

For a view that all this is unnecessary, here's Jobst Brandt's view.

http://yarchive.net/bike/frame_rust.html

So, weigh whether this is a problem of theoretical or practical significance...as well as the value of your piece of mind.

I know, after I've treated frames for rust (with oxalic acid solution) and washed them off, I've used WD-40 (as a cheap alternative I already have) sprayed on the inside...mostly with the argument to displace bits of water, but, after the solvent dries, the remaining oil should give some rust protection. I'm not sure how permanent it is...I also suspect that, no matter how thorough I try to be,there are nooks and crannies of the bike that just don't get any treatment (especially stays). If I really got into it, I'd think simply letting the frame completely air dry before reassembling it is the real trick to preventing internal frame rust.