Traveling is quite easy in Chile, the roads are generally good and there's always food/gas available. From Punta Arenas to Puerto Natales the road is paved (actually concrete I think) and very good (about 250km/155mi), and then you get on a good unpaved road for another 150km/90mi (if I recall the distances correctly). I suggest you fill up with gas in Natales, as there is only one place to get gas in the park (a distance from Las Torres, closer to Explora), and it is expensive and you have to seek out the guy who operates the tank (he didn't seem to be around all the time). Also, I would make sure you have a working spare with you - we had a flat in the middle of nowhere in the park, at dusk - thankfully we had the spare, so it wasn't a big deal. They were able to fix the flat at Las Torres - lucky again, as we had another flat in Punta Arenas the night before our flight back!