I had a situation this weekend. Towing home on 81 in upstate NY. Trailer started to have unusual sway. I pulled off into a rest area to check things out. I quickly noticed the right rear tire was low. I religously check pressures before every trip. Tire had 35lbs in it when it should have had 65lbs. Valve stem guts were leaking. I didn't have the valve guts tool with me so we just went to the next exit and were able to air up the tire to get us home. When we got home I was able to tighten the guts a full turn. Just goes to show you no matter how much you check things, there's no guarantee you're not going to have problems.