Ok,
Guys. Went to the plumber today.
A PVC sleeve is a perfect solution for a case. It's waterproof and (optional) we can have the antenne inside. Or maybe outside. I think you can make a waterproof case for less then $10,-
PVC is realy cheap, there are some PVC screw cap. Waterproof and also in 3rd world country it can be made without a 3d printer....
Cheers.