Probably too late to matter, but...
There may be some misunderstanding regarding the role of humid air. Moisture makes the air a more efficient conductor, which has a couple of positive consequences. It shortens cook times; and makes the temps through the cooker more even. I think the humidity may actually promote crisping poultry skin at a sufficiently high temperature, rather than leading to the usual flabby skin your birds get from a cooker. And, the full water pan also reduces the radiant heat effect from the bottom of the cooker -- further tuning the pit.
Really, there aren't a lot downsides.
I smoked two 14# turkeys on the same shelf in my Fatboy, with water in the pan.
These were kosher birds, so not brined as koshering leaves them salty enough. They were left on the counter for two hours to temp.
I dried them thoroughly in and out, then forced truffle butter between skin and meat along with a few sprigs of fresh herbs. I seasoned further by rubbing the skin with a simple poultry rub (salt, paprika, black pepper, garlic powder, onion powder, fresh rosemary and fresh thyme from our garden); and stuffed the cavity with fresh orange quarters, and fresh lemon and lime halves, a few cloves of peeled garlic, quartered onion, and a few sprigs of fresh herbs.
I trussed the birds with butcher's twine; tying the legs together, and tying the thighs and wings tight against the breast.
The Fat was preheated to 275F with water in the pan. When the birds went in, the pit lost a lot of heat. They were still cold despite two hours temping on the counter.
The temp target was reset to 290F. It was necessary to open the off-side vent wide open until the target temp was nearly reached to compensate; and it still took quite a while to get to reach 290F. Otherwise, the stack was half open, the guru wide open, and the off side (right side) vent was open about 3/4" as well to hold the desired, high temp throughout.
The fire was made with best quality mesquite lump charcoal, plus 1 oak and 2 peach hardwood splits for smoke. The turkeys were cooked to 170 and 175F at the thigh, respectively. Although the birds were the same size and cooked on the same shelf, one was done about half an hour before the other.
The skin was surprisingly crisp and, for once (first turkey in the Fat), very palatable in texture and taste. The flesh was smoky enough without being "hammy," the smoke flavor itself was mostly peach with an oak accent and an undertone of mesquite (as hoped); the meat was tender, juicy and delicious. The truffle butter was lost against the smoke, and while I'll continue to use butter I won't bother with truffles again.
Hope this helps next year,