You don't have much choice but to get the bondo wet. After you get it sanded down, THE ONLY way to remove the fine dust from the micropours is to go over it with a damp sponge or rag, OR hose it down. If you're worried about painting over damp bondo just put the car in the sun for a few hours, then prime. I have NEVER had a problem with moisture bubbles under the paint but I have seen them though. Common sense is the key.
