After inoculating the logs with the mushroom mycelium plugs, I coated the plugs with beewax, as directed by the Fungi Perfecti instructions. I used some beeswax that I had gotten from BetterBee several years back, when I had bees and was making candles, lip balm, etc. You can also use any food-grade wax.
I found this great factsheet with video from Cornell University (my alma mater) about home-farming mushrooms. I wish I took this class when I was an undergrad!