Jesus guys, let the guy build his tank. Drywall screws will not hold the load, yes, but he's considered that already, and by the sound of it, the frame he's building is more of an assembly jig than a structural skeleton. If it were me, I'd use deck screws too, but that's just me.
Andrew: You've built lots of stuff I see, but don't be cocky, I don't know you and/or how much you know, but a tank and a sub box are two different animals. I'm not doubting your abilities at all, but make sure you've throught through all the angles.
Having said that, Kudos for taking a bit of an unusual construction approach. It's nice to see new methods at work, and if you're planning it the way I imagine, I see no reason it shouldn't work. I would actually recommend against the 1/4" skin on the outside of the tank, unless you have a specific reason for putting it there, it won't add strength, and just provides a cozy space for insects and rot between the layers. If you really want it there for cosmetic or insulation or other reasons, i'd suggest painting it with a couple of coats of moisture tolerant, anti-mold anti-fungal paint, so you don't have to worry about it.
Oh and ignore the needles... for some reason certain threads just can't seem to be well behaved discussion, and someone has to spout off at the mouth. Basslover might come off like a jerk, but somewhere in there is just a looney Canadian, driven crazy by Montreal Winters

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