In my opinion, there is little point using desiccant without the humidity indicator strips. Some have O ring seals, which are good only until the connector is dropped on the dirt floor. The seismometer enclosure itself should also be sealed and desiccated if it is in a damp environment. The desiccant needs to be secured so that as it expands it doesn't touch any moving part. If the seis enclosure is tight enough to stay dry, it will also be spider and waterbug proof.
Bugs can make interesting transients.
ANY contamination, like an eyelash, will cause contact. A recurring problem has been peeling adhesives or coatings. These are often detected by strong local vibration, like a good stomp, that causes a transient. I use an inside-out strip of masking tape to repeatedly clean the magnet gap as well as to ensure that there are no dog hairs on the coil. For the home-made seis, another problem can arise from the flexures, especially if they are epoxied in place.