This isnt going to be very stealth so if i where you id go to the store and get some 6' 2x4's and re enforce this thing... somehow. I mean if someone sees that box they are gonna be like why do you keep it?
BUT to cool it better if the reflector has a hole in it for cooling tubes put a PC fan on it with 80-90cfm. Its not much but... hey its something to help you out.
If it doesnt have a hole cut one 3 1/2 inches wide and get a 4" PVC pipe "socket fitting" glue it around the reflector hole and get a 120MM PC fan again 80-90CFM and have it blowing OUT.
get 4" tubing and make a hole out of the box.
Should help a bit.
As for the problem you are about to encounter with having absolutely zero humidity with cardboard get some of the thickest clear or white plastic painters floor covering (also helps with the smell
). its sold at Walmart. 5-9 bucks. then get some Mylar or atleast the cheap emergency blankets that walmart also sells.
All this is what i would do. hope it helps