Well, I don't have a lot of experience myself in dehumidifying a grow room (haven't had any problems yet with mine; knock on wood!), but I do have plenty of experience dehumidifying my laundry room where my dryer is not vented! What worked for me was AIRFLOW AIRFLOW AIRFLOW. In the case of this particular room (a HUGE room mind you), I bought a 20" high velocity metal framed floor fan (I love Lasko fans myself), you know the kind, you turn them on high and anything not nailed down to the floor or wall blows away. Set it on the floor in the middle of the room, pointed it at an open window, and in less than 24 hours my basement, normally a sauna after a few loads of laundry, was the coolest/driest feeling room in the house.
I did a quick search on Google on how to lower the humidity; I saw guys used huge bags of rice (like you'd use to fix a cell phone that got wet), silica packets, etc etc. Seems like a lot of work and huju when you could probably fix it by improving your airflow. In fact that's the other side of what I found in my search; seems most people recommended simply improving your air flow inside the tent. More fans (or higher CFM ratings on pre-existing), better placement of fans, etc.
But that's just my two cents; I'm pretty new to growing and someone else might have something that's more effective for both cost and efficiency.
