I use the Load Warrior and when needed, I have the large Yak bag. In short, I love it!
2 Years ago went to Moab, the down to Phoenix. Went through just about every type of weather you could imagine and not a drop of moisture inside the bag plus it holds a ton of stuff.
With the bag's tie downs designed for the Load Warrior, it never slipped (Even with MY driving through mountain passes) around.
I also have Boa bike attachments and have used the bag with bikes. You can't get as much in the bag when the bikes are on but, it still worked great.