What he is talking about with gravity feed is a charcoal chute like some stand up charcoal units use.
In my experiance once you learn how to load the firebox, you can get extended burn times without the necessity of this. You can also use electronic "stoker" devices which use small fans and computers to force feed the inlet air at a controlled rate to maintain the temps at your desired levels. I have talked to several competition smokers that stopped using those however because the pulsing air action increased the amount of ash getting to their food, and their scores started dropping. These were not reverse flow units but standard flow smokers though. Reverse flow smokers may not see an issue due to the extended amount of time it takes the air to reach the food.