Advanced Auto Parts sells a product called Crystal View.
Do a search in this forum on Crystal View and you will find others with similar results. This process starts out by wet sanding with two different grits, then applying a polishing compound. Then a sealer is applied that fills the imperfections and makes the cover optically transparent. My results were not totally perfect but much better then any of the other products I have tried. Over all I am very pleased with the product. I spent about a half-hour total on the process.