Step 3: Roof, Finishing, and Notes on Use
I would suggest that you paint the inside with a mold resistant paint like Kils. Additional windows can help with ventelation, just remember to put screen over them to minimize the number of bugs hanging out in there.
Also, one thing to consider if you think you may have a water flooding problem, place a cinder block upright in the pit right below the shitter. That way if it does flood, no splashback. Enjoy. Sorry for the poor spelling I'm in a hurry.