The vinyl will be fine, it's
Oracal 651 Intermediate, outdoor rated 5-7 years. Just make sure the substrate (surface) is clean and dry (alcohol cleaning is a good idea and it evaporates quickly).
Once you apply it to the gas-cover, burnish it down really well with an old credit card or something (45 degree angles are best) before you peel the application tape off and you're good to go.
I have plenty of decals on my car and bikes and I wash them often enough without any issues. Never had a decal come off. I even spray Plexus directly on vinyl and wipe residue or dirt off without issues.
I am not sure what kind of surface the gas-cover is....but I think vinyl will stick just fine to it. Certain plastics with a lot of petroleum don't bond well though, so if there's an issue with the bonding it's probably the plastic. If this ends up being the case, I'd get a painted or aluminum gas-cover or get one of those body-colored gas-cover panels from Smart Madness, and then stick the decal on that. Chances are the fuel-door will hold the vinyl just fine.
Also, make sure you apply it in reasonable mild/cool temperatures....not in the direct hot sun at high-noon as it may not bond as well as it could.
Serg! I'll be seeing you and the crew at Smart tomorrow!
