basjoos would be the one to weigh in on sturdiness... he's probably done more with plastic than all the rest of us put together.
For that matter, he definitely knows his aerodynamics and could probably comment on potential benefits, too.
FWIW, I used clear packing tape to form a grille block last year. The adhesive was pretty gnarly by the end of the season, but it did hold up okay from Fall to Spring. Of course, even though almost the entire width of the tape was unsupported, that doesn't compare at all with square yards of plastic being abused by the wind. (Which is why I started with "FWIW."
)
Rick