Thanks all!
Managed to squeeze the Thule box (Adventurer?) around those wide cross-bars. Filled it to the brim with food, beer, wine, and luggage for the 4-day weekend. It worked well...
Going over some larger bumps (frost heaves and railroad tracks) would cause the box to rock enough for something (I suspect the brackets) to hit the roof. The I-25 winds up to Wyoming definitely threatened to push us around a bit. But my worst fears of distributing our 'goods' along the highway weren't realized!
Tough drive on the way home - saw approx. 2 dozen cars off the highway from Sheridan to Boulder - of course, the (FWD - Artic Alpins) Subaru held on tight.