BetterZip has unrar capabilities included that let you open and extract rar archives. To create and save RAR archives, BetterZip can download and install the rar commandline tool from the win.rar GmbH web site or you can tell BetterZip the location where you have it already installed. Please note that BetterZip does not include a rar license. You will have to purchase it separately from win.rar GmbH.
Go to Prefences > Helpers and click the Button Download & Install Rar. Once BetterZip knows the correct path to the rar tool, you can save and create RAR archives as if BetterZip had it built in. RAR archives can be password encrypted and split into multiple volumes.