For the Base you could maybe make a Box of paper cartridges (Like they used for muskets) and Equipment like a loafing stick or a bucket with water to cool the Barrels.

Hm, a Bucket and a loafing stick may both be possible with Milliput/GreenStuff but I think these are both "attributes" of the accompanying crew. I *might* try my hand on a box of cannonballs? Double layered, cut-down coffee stirrers and really tiny balls of milliput? We'll see.