Definite Chubby Spawn location in COC DLC
Upon doing the sidequest "Gas Guzzlers" in Southern Raceway you are required to kill 10 Rakks. Well I noticed that a Chubby Rakk is always present in the first wave of Rakks attacking, and I also got 2 more to spawn while I was doing this quest.
I did some research on Gearbox forums and it seems the Chubby Rakks continue to spawn even after you turn the quest in. A nice little tip for those who are struggling to get a Chubby to spawn, just hope that Gearbox doesn't nerf the spawnrate of Chubbys for that quest/area.