Hollowing a STL

I am a UK railway modeller using SketchUp make to design my buildings and locos.My Layout
I use the OOB plugin as is makes designing brick buildings a doddle. I have tried to pass the message on to fellow railway modellers. My YouTube
There is a modeller who has shared his designs.Thingiverse

My problem is when I import a vehicle STL into SketchUp the vehicle has solid windows and I just cannot to seem remove the glassed area to leave the window frame so it will be 3d printable.
Any help much appreciated.
Test Vehicle.skp (5.9 MB)

When you remove the windows the model will no longer be solid and therefore not printable. You would need to model some interior to make it solid again.
Start here to understand what solids are:

This is a good place to start with the basics:

If I were to print this, I would make it into some separate parts as to avoid a ton of support material.
Wheels, crane and cables for starters…

Thanks for the reply’s. I have had some success with using joint push pull to remove windows but it is not a very refined method.
The vehicles print fine in one piece just the window problem.

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Would something like this work?

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That’s what I am looking for but with the front windows as well.

So like this?

I copied the surfaces of the windows out of the component, projected them onto flat rectangles using the Projection extension from Sketchucation so I could extrude the shape through the cab. I reversed the faces on the extrusion.

Then I selected the extruded geometry, cut it to the clipboard with Edit>Cut, opened the component for editing and pasted the extrusion with Paste in place. Then I selected the geometry of the cab and the extrusion, right clicked and chose Intersect Faces>With Selection. After that I erased everything that isn’t the cab. The part of the extrude shape between the side windows becomes the inside of the cab.

Rinse and repeat for the windshield surfaces.

If your model was cleaner and the components solids this could be a whole lot quicker and easier to do but it’s really not to terrible as it is.

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Thanks very much Dave. I will have a play later. I know the model is not the ideal subject but he has so many ideal vehicles for my era of layout, how could I not have a go at using some of the wheeled ones.