In my experience they are unlikely to be damaged by incidental moisture, whether that be from rain, sweat or the occasional shower. But a single card is small enough that I always worry it will be lost, and it is susceptible to being snapped if carried inappropriately. The Digital Dogtag from N-O-D-E is one of the better solutions I’ve found for carrying a single MicroSD card. It uses a simple spring loaded socket to hold the card securely, and provides enough rigidity that I’m not worried about damaging the card. I added the dogtag to my current APEK iteration this past September and have been happy with the result.