It is possible to create the same solid geometry at the end using either SpaceClaim or DesignModeler, they just have different tools and user interfaces. The enclosure tool is different code in each package, so it might have different results. That doesn't matter, you can use any tool available to make the air solid to look the way you want, it just depends on how much work that will be.
In my geometry, after I made the enclosure, I cut off the air solid before the straws and after the straws to make it easy to see the mesh in the straws and in the triangles. You could put the "plenum" of air before and after the straws back by simply selecting the circular edge and pulling more solid at the beginning and repeat on the other end, then you will have one inlet and one outlet. It would be best to have that be a separate solid and not merge with the 14 air solids behind it.
Another approach is to take the single face of the united 7 straws, and pull that into a solid, then pull the 14 faces of the air forward and you will have a structured mesh for the plenum. When you go to Share on the Workbench tab, make sure to type in a small Coincidence tolerance like 0.001 mm