Neatness is an essential aspect of building a printable or “Solid” 3D model.
The model you shared would become a Solid if you were to clean it up by erasing the myriad of stray edges you’ve left behind and all unnecessary interior faces.
The interior doesn’t need to mirror every detail of the exterior.
That is, modeling a slightly smaller simplified version of just the major features would suffice in reducing the amount of print material required down to a reasonable level.
Here’s what you’re trying to accomplish and a few tools that you’ll find helpful in the process.
A Solid in SketchUp is a single Group or Component whose geometry meets certain conditions.
When those conditions are met, Entity Info indicates the model is a Solid Group or Solid Component.
Also notice Entity Info indicates the Volume of a selected Solid.
• The geometry must form a single* airtight vessel.
Like a perfect soap bubble … •No gaps •No holes •No leaks
• No extraneous Faces** inside or outside the vessel.
All Faces must serve to enclose the singular volume of the vessel.
• No stray Edges.
All Edges must serve to support a Face that in turn serves to enclose the airtight vessel.
Thus, each Edge supports two Faces … no more, no less.
• No nested Groups or Components.
*A Solid Group or Solid Component may contain one or more separate airtight vessels.
**Best that all Faces are oriented Front Side (white) facing out.
Understanding Solid Objects in SketchUp — Aidan Chopra
Solid Inspection/Repair Tools
ThomThom: Solid Inspector²