I've done this. Mine was 3'w x 6'l x 2'h and I grew 8 plants in it for two grows. I can't remember how much soil was in it. But I do remember it was a pickup bed full of bags of Roots Original that cost me close to $300 at the time. I also turned loose around 1000 red wiggler worms in there and used dry nutes. I ran mine as if it was a chunck of Earth, not a container for plants, so I made sure my soil could be reused by not loading it up on salts.
Underneath it I had a tarp taped to the walls so watering the bed wouldn't damage the floor underneath.
After two grows I decided to not grow that way anymore and moved it outside to grow veggies. It lasted another few seasons before the fabric was worn out and all the plastic poles bent and warped. I still have all the unique T connectors though just in case I want to use them to make a small greenhouse or something.
Pro: Every square inch of footprint is room to roam for roots. If you believe in unrestricted root zones, it delivers that. However, that does nothing to improve yield or quality.
Con: Expensive to load, hard to keep consistent moisture, gas guzzler on water, hard to remove everything for a deep clean in between grows.