I can't comment on the plastic media since I haven't used it.
So far as the sand, i think your plan is workable. You need to pay a lot of attention to sealing up the cabin of the car. Sand will get everywhere, I mean everywhere. You need good eye protection, some type that seals to your face with a gasket. Moto x googles worked for me. You may want some type of air supply. This can be as simple as a vacuum cleaner. Prepare to be filthy. Sand in your hair, your ears, the crack of your a**, everywhere. However, the results are very nice.
jt