[tor-relays] Any security tips on running a TOR relay?

Hi, I've got a spare server for two (freebsd) and I'd like to start running TOR relays on them. Is there any security concerns I need to deal with, or is the ports compile + updates good enough to keep my systems decently secure. I actively monitor the machines, but as you know, the game is prevention, not reaction to security incedents :) Thanks, AB49K