Just a question, do you honestly think that spraying over areas of recurring rust a suitable solution to the problem? I find it mad that anyone would spend so much time preparing a car only to bodge something as critical as that which WILL result in a rot box. It might not be a month or even a year but the rust underneath the paint will develop no matter how many 'blow overs' you do.
In my opinion it is not bodjing, it is keeping the car as is. I do not want to change the door when I can repair it likewise the bonnet this would, to me, this is taking part of the origional car away and I would rather keep repairing it as if I do it, nobody could tell know that there is rust underneath and to do this every six months or so is not a problem for me.