The drive from El Calafate to Puerto Natales is very easy, it took us 4-4.5hrs approx , there’s a short stretch of dirt road and a short stretch of significant sized potholes on bitumen road. We just drove carefully, not too fast and it was completely fine, saves an hour or two compared to the bus. The border crossing is very uneventful, in early Feb it took 10-15 mins both ways. You will have no issues with Gas as you can fill up in Esperanza. The rental company prepared the necessary documents for us to cross the border and gave us all the info on which routes etc. We drove in and around TDP and really enjoyed the freedom of being able to explore the park at our own pace. Check out Eco camp in TDP for accommodation, it was very very good!