On the skimming issue, the fancy rust inhibiting paints are moisture curing. They are annoying in that you need to either use the whole container or pour out enough for your work in a seperate container and then throw attempt to save and ultimately throw away the excess. Once they have prolonged exposure to moisture (aka, air), they film over in the container.
I put syran wrap over the container before shutting the lid tight so that they don't become unopenable quart containers.
I don't think there is that considerable of a price difference. $30/quart verses $15/quart rustoleum + primer ($4/spray can)...
a guy on a vw website has some very lenghty non-labratory scientific testing with pictures see link:
rust product thread
