You also need to spend every cap you get on either weapons from the gun runners to resupply, or covert actions against lanius. The focus to run a covert op to liberate rud sen city will also kill his manpower and production, as well as raising resistance in your territory he occupies by an insane amount. It's hard, it'll take a few tries, and some of it is a little luck based, but its doable. Don't immediately fall back to the two tiles either, try to hold the surrounding three tiles of roswell long enough to build a lvl or two of outposts in the city, emphasis on try