A couple small quality of life changes I'd suggest here would be to have the tank be semi-transparent when the player is aiming in a direction where the tank itself blocks he view. The other option being to design the levels in a way to minimize the need to aim low. I had a hard time killing enemy tanks as my tank body blocked a lot of the view, especially the second half of the first level.
Overall, a decent base set of mechanics that could be easily updated to give some really juicy tank combat.