I'm trying to remember if there is any episodes with mini-tanks but I can't think of any, the only thing coming to mind that is vaguely similar would be one of the brain episodes or movies. There is also the Anthology of Interest with big better and a bunch of tanks try to take him down. Those are the only things coming to mind, I frequently watch Futurama on shuffle so if I see mini-tanks or if it just comes to mind I'll edit my post. If you find it let me know as well!