You can run nautilus whenever you want, even when using Openbox or JWM.
Nautilus has a lot more functionality than Thunar, but, to my surprise,
PCManFM proved to have more functionality than Thunar. They were wise to use
PCManFm in LXDE. It is a good file manager.
Rox Filer is OK but I was lazy to configure it. You have to set a certain
file type to be opened by a certain program. In Puppy this fast little file
manager is preconfigured.