The best advice is to keep the inside your home, with the speaker wiring going out through the attic or something similar. If that's not possible, the product below has been used by others around here.
http://www.altelix.com/Audio-Video-Enclosures-for-SONOS-Apple-Amazon-s/88224.htm
I wouldn't leave the amp outdoors on a permanent basis without any sort of protection.
The pool is indoors and the case wouldn't be useful in this situation.
Humidity resistant. Sonos to the best of my knowledge, advertises that the play 1 & play 5 (2nd gen) are humidity resistant. They also warn that the products mentioned, are not water proof.
Moderator edit: Removed advertising link.
