ok whats the deal. i want to put them on a car and i install acrlyic windiows which is plexiglass. whats the diffrence between those and the ones you put on cars? the ones we use i know expand a bit due to some sun and also can bow (bend in or out) but whats the diffrence i belive the car type plexiglass shouldnt do that. how do you keep it on the window? poprivet? thanks in advance.