I have a fabricated steel fixture you can use Eric. I made if back in the old days when the air bag tops popped in. I used it to pressurize the bag to seat the top and check for leaks.

With the air bag in there and a valving arrangement (that you will have to make) to seal the air bag off you can leave it pressurized and roll it around in a big tub of water. I also have the tub.