Closing open solids?

No. Not at all. The Cutlist extension (Hoop2125 is referring to a different extension) will generate a layout of parts similar to what Hoop shows but not as a scene.

You can create dimensioned views of your model and its parts to give you the information you need to build it but do that in the same file as the assembled version. Do not make separate SketchUp files for each part. By using components throughout your model and copying them within the model space to make the other views, potential changes are easily and accurately made. If you decide you need to change the location of the dadoes for a shelf, make the adjustment in the assembled copy of the model. The change will automatically be propagated to all other copies of the component in the model space.

As an example, this is a screen shot of model I did for plans. This piece is featured in the latest issue of Fine Woodworking Magazine. In the foreground you can see the assembled copy of the model and in the background, an exploded view. From these two versions of the model I was able to create the views required for the plans.