Yes. You can select a bunch of incorrect faces and reverse them in one go, too.
Yeah, kind of. In this application think of SketchUp’s faces as the interface between air and the printing media. Anywhere there should be air, you should see white front faces.
Have you found Entity Info? If you select a component it should tell you that it is a solid component or just a component.
A note about what it takes for a component to be considered solid: Every edge in the component must be shared by exactly two face. No more and no less. So that means no edges without attached faces, no missing faces and no internal faces. You can poke through your version of the model to find those offenders. You can’t have a component nested with loose geometry, either. The 3D text in your model is a component nested with loose geometry. If you look at that in my version, you’ll see that the lid geometry is a solid component as is the 3D text and they are nested in the larger component you called …Backdoor…
There were quite a few issues to fix. I did most of them by hand although with a desktop version there are extensions that can be helpful.
You’re quite welcome. And thank you. They told me last week they were giving me a 25% pay raise. Of course I do this stuff as a volunteer so that promise of a pay raise was kind of hollow.
With practice you will start to see how you can model things like this without ever creating any of the things that prevent the component from being hollow or at least you will see them as you create them and fix the problems as you go. Keeping things clean and correct as you go also tends to make the modelling simpler.
Good luck with it. Is this a thing you are just printing for yourself or are you going to be marketing them?