I worried about all of these things before installing 8 outdoor security cameras using PoE. The system is in a rural area with lots of critters and 100+ degree summers. I used direct burial & outdoor cabling but left it above ground and in some cases strung from pole to pole. It's been 3 years and the only issue was 2 cameras shorted at the "waterproof" Ethernet jack connector on the camera.

This was not mission critical so I just "went for it" and it worked out. It was a great payoff since it only took 2 days to mount all the cameras and lay the cables. It would have taken much longer to dig trenches and put the cables in buried pipes. I treated it like a prototype and figured I would improve later based on actual problems that came up.

I did make sure all of the boxes with wire connections, power supplies, and PoE switches were in waterproof boxes and I used silicone sealer where cables entered the boxes. I opened up one box yesterday and not even a cobweb!