Rotopax are the only way to go. Yes, they do swell to the point that it can be difficult to turn the handles to take them off of their mounts, and you would swear that they would explode. I will stop and bleed off the pressure when they get too big. Heat and altitude changes will cause this. Keep an eye on them and back off the handles a turn or two as they swell and this won't be a problem. Full or empty, they will swell. I've tried filling them to where you can't get another drop in them, and the result was gas blowing everywhere when I relieved the pressure from them. All that being said, they have yet to leak a drop regardless of how much pressure has built up in them. I wouldn't buy anything but Rotopax.