I HIGHLY reccomend The Happy Trail boxes AND rack.
I have a set of powder coated tetons and also one one their top boxes on a my '08 klr. The rack is built to be incredibly strong for weight and fall over impacts and the box construction is truly Top Notch.
The welds are very clean, they have proven to be waterproof when I blasted them with a pressure washer, the latches nice and strong and the powder coat is not only attractive but more durable than you think. The hinges are a unique drop out design that allows the lid to act as a table of sorts when your digging though your luggage.
I personally decided not to go with a riveted design such as Metal Mules because I was concerned they may be more prone to develop leaks after being banged around a bit. I figure it will be easier to find a roadside welder for any repairs than a roadside riveter. That said, I have hear and read a great deal of good reviews for the mm's. And I like their on/off mounting system. But the riveting was a deal breaker.
And as far as costumer service the Happy Trails folks have been incredible.
Tim Bernard (founder) really seems to be interested in making purpose built products that stand up to what we put them through rather than flimsy flashy bits that some of the euro companies are peddling right now.
Check 'em out and give them a call, they are happy to talk and IMO they're the most bang for your buck!