This answer explains how the liquid oxygen in a Falcon 9 is evaporation cooled to maintain a temperature well below boiling, by bubbling helium through it.
The temperature difference to the surrounding environment must be more than 200K. How is the tank insulated? What is the resulting outside surface temperature of a Falcon 9 (first or second stage)? I suppose it must be above freezing in order to prevent ice build-up, so the insulation must be substantial, but that seems to be difficult due to the weight constraints on a rocket. How is is that solved? What is the resulting surface temperature?