Hit up this reddit thread : https://www.reddit.com/comments/3ogi3o/
also, after reading that, there is some more discussion on polycount as well as some ue4 specifics as they relate to the technique : http://polycount.com/discussion/155894/decal-technique-from-star-citizen/p1
basically, in a nutshell, you want to use a decal texture (atlas style) in conjunction with tiling base textures so as to avoid the texel density issues that would otherwise arise from trying to bake and unwrap such a large object.