If you aren't removing the brass plugs, then you really don't have any reason to do anything under the handles with regards rust prevention, though a drop or two of TUF-GLIDE or something similar couldn't hurt every few years I suppose.

In regular use, the key is to make sure the blade is wiped dry after use and then protected when "put away." Carbon steel blades are used daily all over the world with no problems and little real attention paid to them other than to ensure they are wiped dry.

It also depends where you live. Out here in the desert, we don't worry about it at all.