Silicone spray? Wouldn't have it near my garage as it's a nightmare to get totally rid of from surfaces, and it wrecks spray paint jobs.
Proper solvent panel wipe is the best thing I've found, but the closest you're likely to have around is brake cleaner - spray onto a rag, wipe the panel down and you should get rid of enough of it to allow the decals to stick with a couple of goes. Thoroughly wash your hands before touching the decals.
And take the silicone & throw it in the nearest bin afterwards...