TL;DR: If modeling with Blender, use the triangulate modifier to reduce the likelihood of SFM messing up your models.

I already posted this tutorial in the Open Source Filmmaker forums, but I thought I could also share this tutorial here on the Blender forums.

I had a bizarre compiling issue involving a model of a bench I was working on in Blender. My bench, a curved shaped bench, looked like this in Blender:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1158252859

However, after compiling the model, the bench proceeded to look like this monstrosity in SFM:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1158253282
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1158254051

It turns out that Source Filmmaker had converted the Blender models from quads to triangles, resulting in these unsightly flaps coming off the bench.

To correct this weird error, you simply need to use the triangulate modifier[docs.blender.org] on your mesh. After using the triangulate modifier, this is how my bench looks like in Blender:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1158269782

And this is how the curved bench looks like in SFM:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1158278506

I've already posted this tutorial on the Open Source Filmmaker forums, but I thought I could share I how I dealt with the problem of backface culling (aka that situation where your models are invisible from the inside) here on the Blender Tutorial forums. You just need to follow these steps:

1. Turn on backface culling in Blender by pressing N in the 3D view. In the menu that appears on the right, scroll down to Shading and check the box for backface culling
   
2. In object mode, duplicate your object by pressing Shift+D. Press escape to leave the duplicate object at the same position as the original object.
   
3. Keeping you duplicated object selected, change to edit mode.
   
4. On the left hand panel, click on Shading/UVs
   
5. Under Normals, click on the Flip direction button. The backface culling should disappear.
   
6. Combine your flipped duplicate object and the original object. Rename if neccesary.

Special thanks to Zappy for figuring this out.