Yeah, I used the black and white poly on the inside of mine. If you use glue to attach the lining, it makes the structure of the box stronger (once it dries). Probly the toughest part of the construction. though (and can get pretty messy).
I cut the door opening, but never got around to attaching hinges. I just made a nice sharp cut, so the door panel stays in place on its own after positioning it properly.. At some point I'll have to add some hinges, but it's been working fine this way so far.
I still have one of the "Shorty" wardrobe boxes from Uhaul. I had plans to use it as a veg/cloning cab (with CFLs or even a 2-foot T-5 fixture), but never got any further than putting together a makeshift CFL fixture (using six CFLs + small clamp-light reflectors) to hang from the steel support bar. Never quite decided on the best means for ventilation for that particular-sized box...but I do think the three feet of height is plenty for raising seedlings and rooting clones, and might even be enough headroom for a 3-4 weeks of veg growth under CFLs (before moving into the "grand" wardrobe box for flowering). AND the "shorty" box would stack very nicely right on top of the "grand" wardrobe box...like maybe in the corner of a garage, or a basement, or in the back of a walk-in closet. They're pretty easy to camouflage just by stacking other boxes around them and keeping them in places where you'd expect to see storage boxes.
I'll definitely experiment more in the future with making other types of cabs out of these UHaul boxes...and even bought a similar-sized (though not quite as sturdy) version from Home Depot. So much easier to work with cardboard than wood...and cheaper too. If I ever get a whole system designed and working properly with the wardrobe boxes, I might consider constructing a sturdier version out of plywood (and alter the dimensions slightly)...but I'll keep working with the cardboard boxes for now. I keep mine elevated off the floor (on a furniture dolly) at all times, so the likelihood of unexpected flooding destroying the integrity of the box and/or creating a hazardous situation with the electrical equipment isn't very high. Having the cab on wheels has its advantages, too, for stealth purposes.