I've decided to store my welder on this chest as well, so I needed to mount the gas bottle on the side. I don't like the typical chain or strap concept and I don't know why that is the standard. I designed and made an attachment bracket that uses the threads for the valve cap.
Supporting the bottle from the bottom and then limiting the bracket from moving in any direction means the bottle is completely contained.
When I told my local welding supply manager what I was doing, he was intrigued enough to give me the cap to cut up for free.
I needed two pins to eliminate motion in X and Y, so I plug welded them in the same plate. The angle, square tube and pin plate were all clamped and drilled for the 3/8" pins in one shot for alignment. One of the pins is drilled at a very slight angle, meaning it will drag tighter as I lift it and not pull completely out without a lot of effort. It only has to be raised about 1/2" to release the the bracket on the bottle.
The safety pin in the bracket just makes it easier than bending over to put a pin in one of the 3/8" locating pins.
Final product
Lower shelf and red angle on the collar restrict the Z movement, the two pins restrict it in X and Y. There is ZERO movement of the bottle. To release it, I simply pull the pin and raise the bracket with the two vertical pins. Then the collar bracket can be rotated out (remember, it's threaded on) and used as a handle to lift the bottle off the cart.
Now to finish painting the drawers and put the top sheet on....
1970 F100 Ranger 2WD
project link: 
Regardless that is awesome