i cook on a WSM. use water for pork butt(lonslo)and foiled pan for everything else(hotnfast).
honestly i think it is just habit to put water in the pan for the lonslo butts. i doubt it really adds any moisture to the actual meat itself.
although, now that i write it out, i think a full cooker of food turns oput better than a single peice alone(could it be the extra moisture from more meat evaporating inside the cooker?)...so maybe some liquid in there would be a good idea.
ok, so that didn't help AT ALL did it?
i'd say just go ahead and add some liquid.
this way, if it is dry you know the liquid DIDN'T help and next time around you can try to cook it differently.
if its moist you got a great meal and can experiment without liquid later on if you feel like it.
"YAWN"-In memory of a friend.