love your process here. i wish i could do stuff like this, i usually get stuck in the first stage (overall shape) and cant think of how to detail appropriately. (also the autocannon arm looks alot like the Alteisens auto cannon fused with its pile driver: [link] )
The design still came out to be AMAZING! 8 hours to finish this piece wow, you're quite a speed painter. I can't help be rewatch the gif it's quite interesting. Hope to see more progress gif from your future works.