To give you an idea: one of the first outdoors WSN I set up was based on WRT54GL soho routers. I bought inexpensive IP54 enclosures from Fibox to put the routers in, and drilled holes and used cable glands for the antennas and power/data cable.
Eight years later they still function just like on the first day . So I wouldn’t worry too much, just buy a good (white!) enclosure and in most climates you’ll be just fine.