I have something exactly like that... I can store two Chucks in it... the trick to not setting off the button is to just turn the Chucks so the button is pointing towards the center of the case.
This is easily done in one of the following combinations:
Chuck + Little Chuck
Chuck + Extra batteries
Chuck + 1 30ml bottle of
juice (sometimes you can squeeze in 2 bottles of
juice or one bottle of Juice and an RCR123 size battery)
Highly recommended, I use mine almost daily or when going out.
With a Chuck + Juice combo you can easily slide an atty in there as well... the Big Chuck sits in there nicely with a 901 or a 510 still attached, although I usually remove mine... the top wont sit flush... but even if it doesn't it tends to fit well enough that it doesn't fall off or slide around.