I'm still a bit iffy about the lack of prep with Krown, I genuinely struggle to understand how any treatment works if the vehicle hasn't been thoroughly cleaned first (as an absolute minimum). The idea that you can roll up and they treat it there-and-then in less than a day seems questionable at best....
Its basically penetrating oil .
WD40 is great for cleaning because it penetrates through oil , mud , water and whatever . Clean up a rusty old spanner and leave it in the garden overnight it will be rusty again in the morning - but not if you spray it with wd40 .
Sunken steel ships submersed in salt water 100 years or more haven't yet rusted away because the process of rust needs water and air .
Krown is a film not a finish , nothing can get under Krown and because its not a finish and you can just spray it again next year .
Paint is a film and a finish so tougher more resilient and longer lasting , but good prep is essential because paint doesn't penetrate so any place it doesn't grip the surface firmly it will trap water and air encouraging and hiding rust .
I had my 80 Krown treated because i knew it would be some time before i was ready to go at things with a wire brush . I didn't expect maybe 4 years and still waiting so i'd imagine most of the Krown is gone from underneath even if i know its still inside the doors and whatnot .
I wouldn't use a sandblaster under the truck because the grit will find its way into bearing and seals and any place you definitely don't want it , i have wondered about soda blasting though and i read about a new process that uses ice as blast media .