Shower leaks behind shower surround

Help please,I just brought home my first Airstream a 98 Bambi 19 ft, was flushing out the water lines, everything was good until I turned on the shower, nothing came out of the wand, but water started coming out of the bottom of the trailer, I took the wand off and tried again, water came out of the fitting, put wand back on, you can hear the water leaking behind the surround when turned on, no water leaks until the shower is activated, how do you access behind the surround? Any help would be appreciated