Hi
I use a 1 litre aluminium bottle mounted on left side of back plate using the Agir-Brokk strap system
Underwater Explorers. Dead easy to install and use.
Sits in snug between me and the wing .. out of the way of any other kit and above the line to my dil cylinder knob.
1 litre bottle lasts 2 normal (< 40m) dives or a 70m dive easily.
At moment I only use suit inflation for bouyancy adjustments and as Dave says, the dil lasts for ever!
Steve