a smaller version of the default tank, with a smaller turret gun size? Something along the size of the Jeep, three seats total, back seat the turret. Maybe shoots grenades instead of tank shells.
While you're at it, an HMG version of the default jeep. Oddly enough no new one has been made since the original version was broken, despite the advent of the better HMG turret.
Other ideas:
"heavy" version of the default tank, with a turret with double barrels (aka slightly faster firing rate)
Flamethrower tank/jeep
Armored Jeep with "gun ports" so people can shoot out of it. It would prevent direct damage to people inside the vehicle.