I just recently finished my rig. Planning to put the tank(3000ci) in my MAP on the back of my vest. Depending on how that works out after field testing, I might invest in a smaller, easier to conceal tank.
when I had an HPA rig, before I went to a spring, i carried my tank across the back of my belt. mainly because I was used to carrying a pouch there on my LBV before airsoft. I never had any problems with it there either with the pouch or with the tank.