Rain Cover For Large Backpack

The main advantage of this raincover is that it is wide enough to cover the tent, sleeping mat and other bits attached to the outside of the backpack. The elastic around the edges is very stretchy and can fit on various sizes of backpacks, and also strong enough to keep the cover in place.

However, there are two improvements I would suggest:
1) When hiking in very high winds, I would like to be able to secure the cover to my backpack, so that in case the elastic does give way, the cover would not fly off completely. Even a plastic clip or loop of string would do the job.
2)It would be good to have one or two drain holes in the bottom, so that if any water does trickle inside, it would not create a puddle.

But otherwise a great functional product!