At it's most basic the AudioMoth can be deployed naked and inside a dry building that would seem to be OK . However for outdoor use a plastic bag is recommended.
One suggestion I have seen is :- "The grip seal bags we just buy on eBay - search for 'Grip Seal Clear Polythene Bag'. The size we normally use are 3" x 3.25". "
I needed a case that is lockable and weatherproof so I've gone for a Samson 1ltr Micro Hard case. I can padlock the case shut and just get a wire cycle lock or python lock through the padlock.
My next issue is sealing the microphone hole in the case to prevent water ingress without cutting out a lot of sound. Now you can get ePTFE seals which look ideal and they are 14 cents each, which is good but the only two companies that sell them have a minimum order of 1,000. Someone posted about acoustic cloth for loudspeakers - which is water repellant and only 12 Euros for a sample pack. The company is called Akustikstoff and the this is the webpage for the cloth. So I now have more than enough cloth for my needs.
The AudioMoth Project is working on a case, updates are posted over on the Open Acoustic Devices website. The Bat Conservation Trust also has a DIY case for it's evaluation project. Also other users post their solutions to housing an AudioMoth on the forums, so always worth a read to see people's inventiveness.
Another housing is described in this paper - https://eprints.soton.ac.uk/432474/2/1_s2.0_S2468067219300306_main.pdf