I figured I had better close the loop on this.
Well, after unsuccessfully trying to buy used boxes on Craigslist and Kijiji here in Ottawa, I decided new was the route to go. I checked out importing for the US (I'm only about 20 minutes from the Ontario/NY border), but realized there wasn't much savings after paying shipping. Too much hassle. I looked around Ottawa, and found RackUltra in Gatineau (a Quebec chain) selling a 'new' Thule Evolution 1600 roof box. I say 'new', because they have had Thule clean off the moulds, and cast it again with only one side opening, and standard U-bolt attachment versus quick release. They have it on now for $429.99. It fit the bill perfectly. Aerodynamic, light, and big enough. I went on Friday, and they had it in stock. Within 20 minutes, they had installed it (corrected a fitment issue, as the box is designed for rails 31" apart, where ours are 32" apart), re-keyed it to match my factory Mazda (by Thule) rack, and sent me on my way. Service was excellent, and install was perfect.
On to the pictures...
And one from the rear...
You can see from this one that width was perfect. All in all, I'm impressed. No additional wind noise either.
Today, I took it off (with the help of the wife to lift it down since it's awkward, and taller than me
). I noticed the nasty wind noise created with the factory rack installed with nothing on it. Luckily, a few months ago, I ran into a Thule clearance sale at an outdoors store in Ottawa (Sail). They had the 42" fairing (872XT) in the bin, and I snapped it up for around $60. I installed it today, and am happy to report that there is no wind noise anymore! Worthwhile addition to anybody running the rack 'empty', so to speak.
All told, I'm a happy camper.
Total bill: used factory Mazda rack ($125) + Thule Evolution 1600 box ($500 with taxes) + Thule 872XT 42" fairing ($60) = $685. $685 is alot cheaper than the alternative, which was going to be an F150 FX2 Ecoboost Supercrew.