Yeah, that'll work just fine, but doesn't scream out, "most elegant, easy solution". That said, I don't know what the "ME,ES" would be.
I think I'd be carrying my tape measure with me as I made my normal trips to the various big box stores, and see if I could stumble on something in plastic that's pre-made and requires just a little modification. Structural plastic tool box, etc.
Pity the milk crate didn't work, but I didn't quite grasp why it didn't. Stick in on the table saw with the bottom up against the fence, with the fence 11.5 inches from the blade....four cuts as you flip it around? Rope handles? Slot cut in the side like your box?
I'd wanna avoid all the cutting, gluing, fastening, priming and painting, etc..
This doesn't help, I suppose.