I've used these on two different bikes for a single night

http://www.amazon.com/Diamondback-Bicycle-Rack-Bolt-Cling-On-Seatpost/dp/B00MJYQ8OW

We could have had more or less weight that recommended--I didn't weigh the packs. Key is don't over/under tighten and secure everything well. Carry the least possible, but the rack you have chosen looks way more secure.