How is it done? Is it a long process? How often?
Once a month we take the front and back plates off the bottom and just sweep out the carbon below the burners. Then we just lift the belt up on the back side and sweep off any carbon on the top of the burners that sit below the belt. No real need to clean the belt, and from time to time i just scrape off any cheese build up (we use shredded cheese) on the belt chassis.
I started this cleaning regime 3 years ago, have not had a need to have a cleaning company come out and clean the oven since. (once a month it adds maybe 20 minutes to the cleaning routine)