I have had several questions lately asking what is the best way to prevent corrosion on the datalogger circuit boards. Even if your boards are deployed in a waterproof enclosure, they will be subjected to high humidity inside the case, usually caused by condensation in the air in the box. Occasionally you might also get a stick, leaf, wire, or something else that crosses the edge of the waterproof seal, allowing rain to get in. Moisture inside your enclosure will cause corrosion.
The first and easiest thing you should try is putting silica desiccant inside your enclosure. The little packages of desiccant come in a variety of sizes and shapes, and they are very cheap. One example would be these that are available from Amazon.
But even with desiccant, you might still have problems with corrosion on your boards so the next step is to use a conformal coating. They come in different formulations like acrylic- or silicone-based, and aerosol or liquid application. Acrylic-based conformal coatings will dry faster and be easier to remove if you need to do repair work to the circuit. The aerosol version is just like spray paint, which is easy to apply but it will probably end up coating places you don’t want to, like screw terminals or the pins of a memory card socket. So I would recommend the liquid version that you paint on with a brush, like this product. Just a few coats of that will add a clear waterproof covering to your circuit board. The combination of desiccant and conformal coating should be enough to keep your circuit happy in just about any humid environment.