The installation of Gentoo SELinux is the same as regular Gentoo. The regular install should be followed from the Gentoo Handbook, keeping in mind the following notes. Then the system should converted to SELinux using the SELinux Conversion Guide. It is recommended to use the hardened stage 3 tarball if you are building a hardened Gentoo system (which is also recommended).

Only ext2, ext3, ext4, JFS, XFS and Btrfs are supported at this time. Reiserfs does not provide the necessary XATTR support, and Reiser4 is not well tested.

XFS users should use 512 byte inodes (the default is 256). SELinux keeps file security lables in the extended attributes, which XFS stores in the inode. If the inode is too small an extra block has to be used, which wastes a lot of space and incurs performace penalties.

# mkfs.xfs -i size=512 /dev/hda3

You can save time by looking ahead to the kernel options required for SELinux, to save compiling the kernel multiple times.