How to do Sub Bass like King Inertia?

I have a background in music but I’m new to beatboxing and recently got inspired by watching Improver’s Taxi beatbox videos and King Inertias GBB compilation. And I must say. when I heard that insane sub bass I couldn‘t believe what I was hearing. I never thought the human voice could make such low sub bass. And his beatbox is so enjoyable to listen to because it resembles music a lot more than being technical.

Since then I’ve been trying for a few days to get that sound out of my mouth but I just can’t. At best I can make sort of a snoring sound while breathing inward and it doesn’t even remotely have the Bassy Chest Voice quality that King Inertia does. Does it involve vocal fry or something? It literally just sounds like chest voice but no way he has a range that low right? I consider myself to have a low baritone voice but the lowest chest note I can get is B1 when I wake up.