I wouldn't trust putting anything on plastic it could stain or even disfigure the plastic
avoid any type chemical base products even house hold products like soap ad such .
that spray on snow a big no no. you never know it could make it into the tank and mess with the fish .
I would be even iffy with those crayola markers on plastic they may stain .
if anything scotch tap a piece of garland around top and bottom of tank , even get some of those static clings for the plastic glass.