Think you'd be better off with something more like a lean to. Something to keep direct rain off the plant, yet still let airflow. With a bag you will seal in any heat from the daytime which will condense to moisture as the night cools.Hey BLT,Theres supposed to be a light rain here 2nite,I went out and put a large black construction trash bag over my last GDP. With the humidity so high here is that a BAD idea???
Hope this helps,
BLT