Southern Gardener,
The reason I ask is, although you have a really nice brooder, it is not predator proof.
Unless you have a big dog that stays outside at night too, varmints can easily go over your fence, knock the top off the brooder, rip the chickenwire off the cage and/or reach through the chicken wire to get to the babies. A hawk can also knock the top off your brooder.
Chicken wire will keep chickens in, but it does not keep predators out. Raccoons have been known to reach through chicken wire, grab a bird and pull it to the fence to eat what it can of the bird.
May I suggest you cover your chicken wire with hardware cloth (small 1/4 or 1/2 inch wire holes) then put a wood trim around the edge to cover up the raw wire edges. Make a solid wood top with hinges and latch it with a bolt or clasp type lock. Put a lock or carabiner through the loop of the lock. Do not use a piece of wood that turns or a screen door latch, because they can easily be opened by predators.
I do not mean to come over negatively, but I have heard from too many people who come home from work or wake up in the morning to find their birds have been killed.
A simpler solution might be to bring your brooder into the laundry room or garage in the evening.
Again, I think your brooder is a great design, but just needs a little tweaking if you are going to leave it outside.