Bubble wrap is easy to install and used by many growers for insulation. Temperature studies show an average of 8 degrees warmer on the north side after insulation.
Install on north side ONLY to ensure enough airflow on warmer days; can still drop curtains on south side. Place between curtain and wire with flat or smooth side toward wire. Use stapes or roofing nails with washers at approximately 10' spacing to hold up bubble wrap, then roll curtain up to start saving fuel and money!
While installing, if you run some of your fans on the south side, the airflow will hold up the bubble wrap while you stape or nail it up. Also, it is very inexpensive, so at the end of winter, just tear it down and dispose of properly. With all of the disease control we have in place, it would not be good management to try to reuse it.