I thought about something as well for the back window after my 300 mile trip this weekend. It was nice outside so I had every window down but I was always worried something might fly out the back window. The only thing I could think to use would be like the nets you see in the trunks of cars for groceries and just cut to fit i guess.
Yeah that's what it's looking like, i wish i had some experience in that area...no idea how to start something like this without a roll of duct tape and some scissors. any ideas on finding the proper netting, mounting theories?