Boeshield was designed to protect planes from moisture/humidity and the corrosion between dissimilar metals (aluminum/steel etc). It isn't meant to protect against salt spray or other corrosive materials/ harsh environments. In my use I have been quite pleased that bare metal items and even painted stuff like pinch welds and door lips never get nasty or bleed rust etc. I use it extensively on unrestored survivor type cars to protect original finishes. It isn't Rusty Jones, but I suppose since Rusty is dead he isn't really Rusty Jones any more either
Now, keep in mind that my cars rarely ever get wet, and never see a salted winter road or anything close. But living in Wisconsin the humidity is brutal and that is why I treat everything with Boeshield. Even though my building has two huge commercial dehumidifiers and was designed for car storage any time you park a car on a concrete floor (in a humid part of the country) you will have issues on bare metal and the like. For example, Boeshield does a great job on exhausts, and after they get hot I will spray them again if the car will be sitting for an extended period.
If you want the ultimate in rust protection the old British "Waxoyl" yellow snot rustproofing is tops, and Eastwood repackages it and sells it as something who's name I can't recall but it is available in gallons and aerosol spray cans. I use a similar product from Wurth that is available in tan, yellow, and now black - it is a creeping snot stuff not like an undercoating. I have a pressure pot gun with a 7' nylon tube attached that has a 360 degree nozzle on the end and can be run down Cobra frame tubes, inside GM doors and frames, etc. This is what I also use on my daily drivers, plow trucks, etc and it is simply awesome. My 2004 GMC has not a spec of rust anywhere and it sees hard winter use. My little Jeep plow truck has been sprayed with this every season and in spring the floors can be wiped clean to expose shiny paint.
It all boils down to picking the right product for the job. Boeshield is great for preserving proper finishes and the like but not for a daily driver. And, I like that it is invisible. Great for aluminum intakes, hardware, bare steel drive shafts, etc.!
Hope this helps.
Colin