beckie, sals have to catch worms in the wild, when we're not there to feed them, right? and the "little presents" are just dirt and a bit of nitrogenous waste. as long as the tank is ventilated like normal, i wouldnt worry about fumes. think of how many worms are in the soil in your yard. do they create fumes? as long as you keep the soil at a good moisture level, you neednt worry about mud. just about "restocking" worms after a while.
best of luck