I don't know about Aliner dormers, but for leak fixing in general, get out the hose and sprinkle the side of the trailer that leaks, so you can figure out where the water is coming from.? The water will cling to the lower side of the roof edge, and splatter right into the corner.? Any gap in there will leak a lot.
If one side leaks and the other doesn't, compare sides and see if there's a piece of weatherstripping that fell off.? Another good test is at night, shine a light from the outside, and have someone on the inside see if the light comes through.
Corners are notorious for leaking.? Many people have to add more weatherstripping.? The rectangular hollow tubular stuff works best, since it compresses easier.? Get some from an auto parts store.
The adhesive on the back of the weatherstripping doesn't last that long.? Get some Permatex Weatherstripping Ahdesive and glue the weatherstripping back on if need be.? That stuff lasts a good long time.