At first, everything looks perfectly fine, exactly as i want it to look like, but in the last seconds, when the camera moves to the side/the backside of the object, you can see through the walls. You know what i mean? You can read the "austin, texas" type on the topside, even though it shouldnt been seen from that perspective.
I created the whole thing with 3d stroke and some instances so it looks like 3d. What I simply don't get is why it doesn't appear as a solid object, but transparent from the sides. Is there some way to set this straight?
Try moving the "Austin Texas" text layer below all of the other 3D layers. 3D stroke and Particular are 3D effects but their 3D worlds don't mingle with other 3D layers in your comp. Basically, they behave as if they are a flat 2D layer as far as the layer stack and 3D space are concerned.
OK, This is kind of tricky but I played around with it a bit and I think I've got it figured out. You need to put one copy of 3D stroke behind the text and one copy in front of it and then adjust the top strokes Camera "Z Clip Back" value until you can orbit around it and you don't see any more problems with text showing through. 431 is the value that worked for me. If set the clip value too high it won't work right either. Basically the clip values will cut off the stroke at a certain distance from the camera so that you can fake the 3D layer interaction. If you turn off the bottom 3D stroke layer you'll see exactly what the clip parameter does.
Here's my layer stack and I've uploaded my test project as well.
No problem. Just keep in mind that the Z Clip is based on the distance from the camera, so if you move the camera farther away then you'll have to keyframe the Z Clip value. Or it might be easier to just skip all of that and just use masks with a track matte on the top 3D stroke layer to get rid of the parts that are overlapping the text.
If you open the project file that I posted you'll see that it does work if you orbit around, but as soon as you dolly or change the distance of the camera it no longer works. Just turn off the bottom 3D stroke layer and dolly the camera back and forth and you can see how the clip parameter works.