PaulCW,
You purchase through a dealer. See the Purchase Local statement on the Grand Design website. I also suggest you take a look at the
Grand Design Owners Forum. It will give you a good feel for what owners think about their units, and customer support (excellent).
The GVWR is 1500 more on the Silverback. We eliminated it because we could not get to the refrigerator with the slides in. It also didn't give us any good large storage spot (think 20# bag of dog food), a spot for the dog water bowl without kicking it over, or large enough spot for a clock radio and glasses by the bed. There are other differences too, like the hydraulic slides on the Silverback.
We didn't find a small enough Laredo (any better than the one we had), and just didn't like the feel of the Cougar. The Mountaineer was too heavy. We considered a Montana High Country, but one floor plan had very heavy recliners to move to put in the slide and the other had a walk through bathroom with a clearance about 3" shorter than the DH. With our trade, we were quoted within $100 difference between the High Country and Reflection (3 different quotes) - all at different dealers.