I have a blow molded part I need to create a nest for.  It has imported from my customer with just under 5900 unique surfaces.  I've tried all the usual ways to create a solid from the surfaces, but keep hitting road blocks, the biggest of which is it takes massive amounts of time to do anything.

Here is what I've tried:

exporting as a step and reimporting

Knit surfaces while ticking the create solid and merge boxes

delete and fill

thicken

I've not gotten far with any of these before I have issues. 

Has anyone else had this issue?  If so, how did you solve it?

I should also mention that it started as a parasolid and imported as an assembly with just under 5900 part files, which when opened or sectioned are simply surfaces. 

The end goal is to simply create a cavity inside the nesting block but I need a solid to do this as far as I've ever known.  Perhaps there is a work around for creating a cavity using a surface?