...I'm NOT looking for a case that'll protect the contents, is airtight, or anything of the like. And Pelican cases are also nearly a full inch thick on all sides, so I'd end up gaining no volume versus the thin-walled blowmolded polyethylene case I'm using now.
My costuming gear doesn't need to be protected against shock, fall, or destructively abusive impact. I do that to it every time I wear it, by and large, be it just running around, ice-skating in it or power-sliding 20+ feet across a floor on my knees.
I'm trying to get more internal volume so I can reduce one costume from two cases to one, and pack more accessories with another to start; as much closer to the maximum allowed 8000+ cubic inches limit airlines allow before hitting oversize-baggage limits on airlines. Somewhat stylish, functional, and visually distinctive are giant bennies versus having Yet Another Of The Same Case As Everyone Else rolling down the conveyor belt.
And I explicitly said I DON'T want wood, FRP (fiber reinforced plastic, I.E. fiberglass/carbon fiber) or other "brittle" materials that have a failure-mode or wear-mode of splintering.
Outer Dimensions of the case MUST sum (raw length + width + depth, NOT UPS/USPS/FedEx girth + length) to less than 62. I'm opting for '20 inches cubed' as a nice, simple figure to work from, especially since a cube is the optimal set of sizes for maximizing volume of a rectangular prism. Might be 'outer wall thickness * 2' over that in each dimension easily, etc.
Weight MUST be under 25 lbs. 8000 cubic inches of my stuff weighs about 22lbs, so that'll give me a few pounds lee-way before the weight-cap for 'overweight baggage' of 50lbs. And yes, I realize this means the case will weigh more than the contents. Fabric, foam, faux-metal and faux-fur trim accents are low-density high-volume stuff.
Case should be thin-walled to maximize internal volume, as it does not need to protect the contents against impact, shock, or the like. The contents are safe against those.
Case needs to be sturdy enough to have about 250lbs set on it briefly, or about 100lbs set on it indefinitely. AKA loaded in a plane's cargo hold, and sat on as a chair briefly in the field in a pinch. The thin-walled blowmolded case I have now can handle this, so I don't believe this is unreasonable to expect from something likely made of 14-gauge aluminum or thicker.