I have written a complete guide to creating custom CSG mods using 3DS Max. I'm still working on the phrasing in the tech-heavy parts. I believe the information presented to be correct, but there may be errors. Happy to receive any questions or feedback here. https://docs.google.com/document/d/1Blptknucz0uRbAvAIyq2ynCOD9TVVGWjHr-DhUQKe7M/