No need to bother with masking tape. Doing it your way is way too much work. First you have to apply the tape, then you have to trim it, then you have to mask off the rest of the body and then you have to paint the top! And besides, the texture of masking tape doesn't even look like the texture of a vinyl top.
My way is much easier: mask off the body and spray the top from a distance, so that you create "orange peel"... the texture will look like a scale vinyl top. You can spray the "vinyl" any color you like, even if all you have is gloss, because you can shoot a coat of semi-gloss clear over the top to simulate the "vinyl" sheen. If you want even more realisn you can create the "seams" with thin strips of tape or styrene first, then paint your top. You could also try "faux fabric" texturized paint.