First of all, proportions are fine in this version. I also understand the tank tray now, this is a nice idea! I just realized reloading the gun isn't easy due to the handles and the weight so a quick-load system like this has its advantages. I still think the axis/mount looks a bit too filigree and that might be solvable by increasing the width/radius of the elements but I understand that this might not work too well together with the way the tank tray is supposed to function. The part of the tray/mount with the sliding element (left side) could maybe profit from a more stable appearance though. The one on the right looks quite stable due to the reinforcements with the khaki material.
So let's enter refinement phase! Here are a few more suggestions for detail work: