FWIW; I used a large sheet of Bubble wrap to put over my screen & side windows for last winter & it worked really well. It won't act as a black out unless you add something to block out the light, but it was cheap (err, free actually, as it came as packaging on a telly) & easy to do. It save me using my genuine silver screens over winter which could well have damaged them. The wrap was undamaged & has been stored for use next winter.
Place it across the windscreen & open the doors, tuck a large triangular dart behind the pillars so that the rest of the wrap goes straight across the side windows & there is a few inches to tuck round the edge of the door & then shut the door. You may also need to cut a slit up from the bottom to accommodate the wing mirrors.
A bit of black poly sheet & some duct tape could produce a "Black Screen" that would be as good as the real thing but 100 squid cheaper! Just a thought for the financially challenged campers.