This is the LH BMW bracket. The bag has an approximately 8" long 'finger' that hooks over the horizontal bar at the top. The square pocket at the bottom-left is where the lockable latch clips in.
:beer: on that!!! I don't have much experience riding in cold weather, but my camping experience tells me that a single layer of cotton will make you freeze your tail off!
Layer with synthetics, silk, or wool, and you will be much better off.