I make all of my own from scrap OSB pieces picked up off of construction
jobs around the area. All are built exactly the same size.
With 42 working does, "time" is important for a smooth and efficient
operation. All of my brood cages have the exact same sized door.
I can pull the box out of the cage and it'll wedge into the door
opening. That way the doe cannot interfere with whatever I'm doing.
I keep about 30 boxes on hand at all times. I've never used them all
at the same time............but I've came close a time or two.
I use two 6-penny box nails driven into the front edge of the box
with the heads cut off. I leave about a half-inch of the nail exposed.
When I slide the box back in, I elevate the front portion till I get it
where I want it to go, then lower the box. The nail-stubs will go
through the floor wire....Locking....the box into position. The doe
cannot move it.