i called ims myself about this a year ago and they said the same thing. a small amount of fuel goes threw the plastic, which ruins the adhesive on the decal. thats why race fuel is stored in steel containers vs plastic. ims told me that you can paint the tanks but all the fuel has to be out of the tank and to leave it outside in the sun for a day or so, that way all the vapors are totaly gone. then paint will stick, if you try to paint with fuel in the tank it will end up failing. i gave up and left the decals off.