Creating Custom Models / Custom Materials | Half-Life: Alyx | Source 2 SDK
I hope this tutorial helps some of you, leave any questions down in the comments and I'll do my best to answer them. Good luck!
Also, forgot to mention! You can add a collision mesh by clicking "+Add" in the ModelDoc editor, and typing "Hull", if you click on "PhysicsHullFile" you will be able to import an FBX as a collision hull, which makes it extremely easy to create game ready models with minimum suffering.