We were concerned about fan noise when we heard the furnace on our soon to be built 21' was being moved from the dinette to the nightstand.
However, we have run the furnace several times and found the noise low enough to not disturb our sleep; it's audible, but not too loud. As mentioned above, the more central location seems ideal for distributing the heat throughout the trailer.
Reace's solution of raising the nightstand counter enough to install a second drawer, so the furnace in the nightstand caused a loss of only one drawer, seemed the best design compromise to us.