Yes, it would work in the same way as my rain skit and long waterproof jacket, You would save some weight as well, except it would not work if your waterproof trousers had full length zips down the side. As I've experimented in all sorts of ways to keep dry I did have cheap Peter Storm leggings and cut the legs short to just over the tops of my gaiters, they work fine. I personally prefer gaiters on the lower half of my legs than overtrousers, they are easier to manage, (and help my legs to stay cooler) when having those days when it rains, stops, rains, stops etc.