Well, in my opinion, villages didn't have to have a fort or anything that serious. This, of course, strongly depends on the setting: a viking village and a late medieval village deep inside a feudal state are pretty different. Adding a keep shouldn't be hard, but I think it would make a village look less "villagy", almost like a town or motte-and-bailey. What I am going to try is to add a palisade as an option for the outpost feel.