Thanks, its really cool! And you're right - vehicles protecting you when there is no one inside is really good, especially for 0.15 where turret creep will be massively nerfed (I heard that turrets will have arming time after being placed). What really needs to be done though is basic awareness for vehicle AI's of each other's collision boxes, so that when you drag select units and order them to go someplace - they don't try to occupy same tile ramming each other to death... Don't know how hard that would be to implement though.
Vehicle AI reacting to enemy attacks that outrange its main weapon would be nice as well (for example chaingunners moving a few tiles forward to retaliate against big spitter, that has better range and is attacking it). Late game its main reason why gunturrets lose their usefulness - enemy too often just ouranges them. Making them react to that would let them be equally useful at any stage of the game.
And also its just my opinion, but getting chain gunners without even having access to engines is kind of strange. If it was me, I'd make them available after automobilism research and at least use 5-6 engines in crafting recipe. Makes more sense.