RabbitVCS is in Gentoo portage since 2010-10-26 (thanks to Rion and Gentoo devs). So the installation is quite usual.
emerge rabbitvcs
Check USE flags before, may be you will find something useful for you, like “cli” interface.
RabbitVCS has several dependencies that may or may not be easy to setup on Gentoo. For a list of generic programs and libraries that must be installed, see our Minimum Requirements. You will need to determine the correct Gentoo packages for each listing.
One you have satisfied all dependencies, download the tarball and from the top folder type:
sudo python setup.py install
Once that is done working, look in the clients folder and read the README file for each client/plugin to learn how they are installed.
Installing from trunk or from a branch is relatively straight-forward. First, install the dependencies listed above, then follow our developer installation instructions.