Here you see the metal sub quick release mounted to the case. I use this system because it has a universal character. You can easily mount 3 - 5 7 or even 10 liters or a battery pack to the case.

Metalsub calls this system ponybottle quick release

Here is the inside of the case. I made two rostfree plates (AISI 316) to reinforce the connection.

Because the nuts use some space I added two rubber straps to support the bottle without being damaged.

If you have other pictures or ideas on offboard gassystems please send them to me!