The Kerbal train (36 Kerbal) a bit hard to turn but works it is based on the design from before. As i said it is extendable. The basic design is as follows: 1) M-Beam 200 I-Beam Pocket Edition as the base of the rover (or longer version but need more wheels) 2) attach solar panel on the end. (with snapping) 3) attach Battery to the bottom beneath the solar panel and rotate so that batter locks up (with snapping) 4) attach wheels (no snapping) as high up as possible. 5 fine rotations down from the parallel allignment of wheel and i-Beam 5) attach Command seat from the bottom and turn it up (like the battery) (with snapping) 6) good to go (dont forget to disable the wheels steering in the back for better stability) 7) if there are problems (rover does not move, problems with terrain) rotate the wheels a bit more i found that the longer versions are stabler than the shorter versions if your are going for the shortest version i think you could do the same with two octangonal struts the real limiting factor in diameter are the wheels.