here's a pic of the old epic mini for your consideration...
silver tower
you can see the guns poking out if the towers themselves.
but how's this for a twist...what about not having any guns at all but instead representing them with sorcerors? you could have a few individual sorcerors dotted about the ground level and a lordly looking guy surrounded by a cable of lesser thrall wizzards on top of the main tower for the largest tower. just a thought
what are you gonna do for the base/mount? are you gonna try to have it kinda floating above the table, with the under side modelled to look like the thing has been ripped out of the bedrock? that would be such a cool look!