I am in agreement with everyone here, a cardboard box is a fire risk
I always tell people who want a discreet grow to go to the local junk/charity shop and buy an old wardrobe to convert.
you can pick them up really cheap, and they are much better than the new flatpack stuff as they are made from real wood, which handles moisture and temperature changes much better that the poorly made wardrobes of today. Plus they are discreet, nobody would look twice at an old wardrobe, but a box construction or a grow tent stands out like a sore thumb
If you pick one up let me know and I will see if I can help you with the converting process