Yep. Simple solution is always good. Where are the curtains? I don’t see them in the pics.
before painting, I’d try using cardboard and zip ties one of two ways.
1. Cut flat piece of cardboard into size that will fit over crate opening, add holes to zip tie on top of crate. Cut a hole large enough for chicken to get in, and to provide a 3-5” lip to keep in bedding. Place this onto crate on its side, so the chickens walk into crate. The opening could be a circle or triangle.
2. Keep crates in upright position as they are shown in photo. Get box that will fit over the crate with enough height for chicken to get inside through the opening you will cut on one side.
you could do two crates one way, two crates the other and you may then have created two favorite boxes, rather than one.
our chickens really like the kitty litter boxes, but not all of them do. Some definitely prefer the other boxes (larger and darker). But we have two of each type and there is a favorite box of each type. Maybe offering two styles will get them to spread out a bit.
Good luck.