Your concerns are well founded. There have been plenty of successful cardboard box grows, but the way I see it, you have enough to worry about growing an illegal plant.

Check out some second-hand furniture stores, I'm sure you'll find something suitable. Just remember that you'll have to make some holes in it (intake, exhaust), so choose wisely. It's definitely worth the little extra money. Plus you have a better chance of making it stealth.

I'd recommend getting something a little bigger than you think you'll need. That way it'll be easier to scale up and fit other things in there (carbon filter, inline fan, oscillating fan, reservoir, more plants, etc.)
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