Rub, I'd be much less worried about the water not seeming to evaporate than it boiling right out. I'd put your water pan pretty much square in the middle of the smoking pit, maybe a tad left towards the firebox. Since I don't see a water pan on the assembly instructions from Brinkmann on the pit I'm assuming this is just a pan you've added.
The sole purpose of the water pan is pretty much to hold the temps constant by absorbing spikes and releasing heat into the chamber when you need to open it. The steam isn't really what's keeping the meat moist, thats the lovely boiling fat in your meat.
Many have even converted over to sand instead of using water as sand is a very stable heat sink and doesn't need to be refilled.
Good luck to ya.
Neil -- "Easy Bake Master"
NB Bandera [gone to heaven...conveniently located in Long Island, NY]
Rebel 23, WSM A, WSM B, UDS, Easy Bake Oven
Pork Pistols BBQ
MOINK...It's what's for linner.