If you are planning to take your trailer into the mountains there are a couple things you need to think about.
Take a few extra precautions.
Go down the mountain no faster than you went up. Your trailer will be pushing you along, take the terrain at a slow but controlled speed. Use a low gear.
Avoid riding the brakes on the way down. Doing so can cause your brakes to fail. Rather than constantly stepping on the brake pedal, you should slow to a safe speed and then ease off. The brakes need to cool and then you can depress them again.
Make sure you stay a safe distance from any vehicles in front of you.
It is better to go slow and be safe than save three or four minutes on a mountain grade.
Check your weather forecast before you go.
Remember that mountains put extra wear and tear on your vehicles. Make sure all components are ready.