The Youtube video showing the AA N3 shows it on the beach :-)
https://www.axiomaudio.com/wireless-speakersI like Ian's answer but I'd still take a few precautions as the front USB/Ethernet ports are only covered by a small flip door (I'd consider taping them for a better seal). Same would go for the rear input jacks.
Disclaimer: I don't own a AA N3 but have used my Sonos Play:5's for a similar purpose. I don't think the P5's are as water proof as the AA but they have gotten pool splash and beverage spillage on them to no ill effect. Enjoy the portability!