As mentioned, a suitable enclosure would definitely be a good idea. An enclosure rated as NEMA 4 would be perfect. This is suitable for outdoor use, and there are plenty available, many shapes sizes and styles. Digikey carries a quite reasonable BUD line that has models with PCB mounts, clear lids, solid colours, etc. Even though I often use a NEMA 4 rated case for many items, I still protect the PCB with a conformal coating. This helps with condensation during temperature variations. the spray I listed will coat MANY PCbs, it goes a long way. It is easily repaired if changes to the circuit are required.
Most generic RTV silicone contains acetic acid for curing, this is what attacks the metals, especially copper. Some silicones designed for aquraiums, etc use other curing agents, and may not be as harmful to copper. This is still a very messy alternative though, and likely to be more expensive than just using a spray designed for the job.