WaterDexSprinkler Timer Remote Control

I recently installed a WaterDex provided by our local water district in CA. My timer on an outside wall, and because neither receiver nor transmitter are waterproof, I installed an additional waterproof box to house the receiver(timer box did not have room to place it inside). After linking units, I placed the transmitter about 15 feet away in an outside window. Within a short time the link was lost. I relinked the units and placed the transmitter outside on top of the timer box...again the link failed. Not a very impressive start up.