How about a MLRS based on an AAV7?
A single six round unit stowed horizontally in the cargo / troop compartment and raised to fire, exhausting through the not completely lowered rear hatch to permit the vehicle to traverse to aim.
Fill the cargo bay with Spike ER.
Horizontally stowed, vertically launched SAMs of different types.
Light weight 105mm turreted gun.
Retractable 155mm open gun but with auto loader.