Scarily, BA Tube Artillery is only 27 BV and doesn't roll on the cluster chart when it hits a hex: they ALL hit the hex. I think that's WAY more broken than any BV measure ever could be... ;)
Light BA is the minimum size necessary to mount the thing, since it's 4 spaces, and has to be in the body. After the tube and chassis, you only have 150 kg to work with for armor, ammo and maneuverability. Totally doable! :D