It is possible that the lenses will become dirty from the outer side. Wipe them with some soft rag and be careful not to scratch the surface. Nevertheless, they must be really dirty for the signal loss to be observable as excessive packet loss.
Maybe the sillica gel will eventually become saturated from the trace humidity that leaks inside no matter how it is sealed. It will probably manifest as high packet loss on a sunny day after rainy one and it will be possible to see water drops hanging on inner surface of the lens. Then tear off the sealant around the cap, unmount the cap, remove the silicagel, put it into oven (minimum setting for gas oven, 150degC for electric oven, do not use microwave oven) for two hours, replace the bags, replace the cap and seal it again with the sealant.
What to do if one comes is described in a FAQ entry.