Install new cab over curtain in a Bigfoot TC, HOW?

We have a B+ and to block out the light, I used a tension rod across the cab then used a heavy fabric for my curtain. Don't know if that would work for you, but it didn't required any screws, etc.

When we went to Alaska, I bought us sleep masks. They were very light weight and we got used to them quickly. They worked well.

Dale