Or if you are doing a bare base, just drill a small hole in the bottom of each wheel and insert a pin that has a matching hole in the base. Just enough epoxy to get both sides stuck, and you are done.
By the way, who makes the kits that you are working with? I am currently working on a large Civil war era cannon out of wood (cherry and mahogany). It isn't perfectly to scale, as I am eyeballing everything, and it is more just fun time between projects at work. Total length of the carriage and barrel together will be about 16 inches, with a wheel diameter of 8 inches.