Why do actors make up in the RV or in the makeup hotel?

Because it will be more convenient and quick for them to change clothes in the RV anytime and anywhere.

Many stars filming in Hengdian will prepare an RV, and they can get on the bus at any time to enjoy the one-stop service of air conditioning, makeup, rest and eating. If you go to the hotel, it will be more troublesome, and the distance may be far. Actors often have to change clothes and can't run back and forth, which will delay a lot of time. Another thing is that the hotel may not have all the facilities like an RV. So most stars will bring their own RVs.