I prefer to use a small kethane tank and convert it into larger fuel tanks, to me it seemed more efficient for the weight/space. If it stays in place once its on the surface you could always attach disposable thrusters on to it. Pop them off when it lands. Lots of ways of doing that. If the size is a problem you could having dock ports attached to decouplers, so you could add the thrusters in orbit and dump the ports and thrusters once you have landed.