When you have a model that is not a solid part, (think a transmission case without any guts inside)  but a thin walled "casting" that has machined internal volumes and geometry, and you only want to get a cavity of the outside surface for a mold of the outside surface, the Intersect tool ends up giving me all of the internal regions of the model, even though I have closed off all openings in the part, via extruded and merged bodies created at each opening,  on the model itself.  (at this point, the model should very well be "watertight" as if I were surfacing a mesh.)  When I subsequently use the cavity command, or the intersect feature, I still end up getting all kinds of regions for the inside geometry within the closed off model in the "exclude/include" list in the property manager.   All of the tutorials use simple solid parts like an eye bolt with no internal volume or any complexity to the geometry.  Is there a way to force the intersect or cavity tool to ONLY deal with the OUTSIDE surface of a model so that when using the intersect tool, or the cavity tool, it is ONLY referencing EXTERNAL geometry of the part, and not giving me 60 regions of various volumes within the inside of the transmission case? At this point, the display itself of these internal and external regions make it impossible to select each region and even tell the difference between it and the external region in the display. (simply too much information with multiple regions being displayed, slows SW down to a crawl to render the display of any of the regions)...

Thanks for any advice, and best regards to all.