I use Copic Markers and similar alchol based markers with both blank plastic crankbait and soft plastic (mainly with a white coloured base), and with both raw materials the same tecnique, that is I spray the markers with Spritzer, a handly pump. In such way you can better control the quantity of color and create texture like those made with an airbrush, even if it isn't so accurate.
With plastic crankbait I seal the paint spraying Plastidip clear, with soft baits the cold coat 50% MEK + 50% PVC Glue.
Spritzer Pump is really funny to use.
Bye.
Cami