Our side curtains closest to the front bed have often been wet, but we discovered that this happened only when TM was in down position. Heavy rains with TM up did not bring about wet curtains. We ruled out water coming in through the walls and roof. We eventually concluded that with the TM in down position with front end lower than rear end, water on back of roof runs forward through several spaces under the bag seal possibly at very center of top and sides. Our theory is that this water puddles on the back roof and with roof sloping towards front, water can only run off the edges of the lower roof. That is right by the front side curtains.
The solution which helped us is to keep the front end of TM higher when parked in closed position. When washing TM in down position, we are careful to have TM front end raised to prevent water running toward the front.
Harmen