I am working on nestboxes. Gonna rearrange coop and put in proper nest. I kinda went extreme

4x4 ft with 9 cubbies roughly 15x 15.
I built it yesterday in my living room.
Gonna demolish what I have in coop, move it out there.
I do have kinda an issue:
It doesn't have a back on it.
I don't have plywood (even a sheet of paneling would work, no way to haul a 4x8 sheet, only need a half sheet(4x4).
Not gonna go buy a half sheet.
Can I cover the back with plain ol chicken wire? It will be in a secure coop. Does it even need a back?