OP, fortunately it seems that the sporadic weekend closures of the RER to the airport are finished. I'm not a huge fan of the Roissy Bus comfort, but it is direct. But remember that the RER isn't prone to delays from road traffic should something freaky happen one Sunday morning.
Originally Posted by
NickB
As others have suggested, it would make more sense to get the RER A from Auber than faffing about with the métro. At Châtelet-les-Halles, the connection to the RER B to CDG is just across the platform.
Actually, since you will be heading south on the RER A and then north on the RER B, you can't just walk across the platform to transfer, but will have to go up stairs/an escalator, walk 10 meters (30 feet), and then back down stairs/an escalator.
Originally Posted by
wendySFO
Haven't done the PER to PER transfer at Châtelet-les-Halles as I prefer no transfer if there is a direct route. Also taking the metro at Tulleries is closer than walking to Auber, though I now learn it is probably end up the same as PER to PER transfer is easier at Châtelet-les-Halles. I may give it a try if expecting traffic in the city/highway.
As
NickB said, the train is called the RER.