( My opinion only ) A vent hole is still needed in any and every tube Mod bar none, my opinion of catastrophic = is a mod blowing up in ones face, the gas pressure alone from Batts going into thermal runway could make a mod blow up just from the pressure alone. This is even further dangerous with that second tube screwing over the first tube. A blow off feature or not, no body knows what could happen if a batt does go into thermal runway because the same thing isn't going to happen every time and people will use different Batts now that it accepts them, you never know what can happen when different Batts go into thermal runway it's going to be different at times what they actually do, especially when enclosed in a tube, a double tube cover is like a pipe bomb waiting to happen. At a minimum there should be a vent hole in the bottom of each tube for sure! Again my opinion only.