I have sprayed down my '87 religiously for years, and it seems to have slowed rust down. Especially make a point of making sure the fuel lines, brake lines, and known rust traps (like around the fuel tank) stay nice and greasy. Not a permanent fix, but keeps the decay in the bodywork roughly similar with that of the running gear.
Tried Krown this spring and it seemed to disappear awfully fast, like it was too light. Must be a nice penetrant though, if it could be covered with something heavier.
When I used to go traveling for half the year I'd park my old '72 510 (510's were notorious for rusting into nothing) and check how effective my 'treatments' were when I got back. Engine oil was 100% effective with the car sitting like that, WD40 was useless, you could see the rust growth.