As with the rest of this glitchy piece of shit dlc there's no reason for them to explode ifyou dont bump them into each other. I'm sure the hit detection is probably off or something. I'm glad it helped you once you got it to work though. :-)
For anyone else that tries this method, it helps if you crouch while you're releasing a tank and make sure the tank is upright not at an angle so it won't fall over and bump another one.
400,000gs reached 1-13-15. Used D4 to get it (get it, it has 4 in the name) due to my disgust with how Halo: MCC has been handled. Achievement used for 400k milestone: Business as Usual.