The Krylon is not fuel safe.
When I do inkjet printed decals, I use Krylon Crystal Clear on the entire sheet after printing and before cutting out individual decal footprints, otherwise the water would disolve the ink.
The Krylon simply protects the ink for the water slide application.
After the decals are applied, I use two-part automotive clear over the entire model (PPG).
I've only done relatively small decals, so can't comment on larger surface area applications, although all the small logos on the tail of my "New Spirit" Lancair is one big decal.
Paul