I have used a double layer of 3/4" bubble wrap for 2 years now. Works very good. Comes in a 4' x 250' roll for under $100. No mold issues, great diffused light, plants are A+++ with no shade cloth needed.
I do however think using bottles could work extremely well if care is taken in installation. I would only used bottles with caps, labels removed and no tape as it will deteriorate in the heat. If you are concerned with the air gaps, then maybe put the bottles in a zip lock bag first.
Best of luck and may your experience be fruit for all those who follow.