It could also be made to be painfully obvious unless you put some effort into hiding the artillery, while still remaining within the short range of its gun. Like this:
From above it'd be a giant neon sign saying "shoot me" and/or every time it fires the recoil would send up a big dust cloud. It'd be skill based to be able to fire off more than a few shots, really balancing out however big of a gun they decide to put on it.