I see something similar as a temporary pit for church fundraisers in Western NY.
There is a company called Chivett'as BBQ that puts down a base of 1/2" steel plate and build a pit 4' x 24' in the same manner. They use charcoal as a base and as the food cooks and the charcoal gets weaker they will add charcoal to an 8' section at a time to keep the fire going without interruption.
At many locations they successfully turn out over 500 chicken dinners in just a couple hours. People travel for miles for their signature vinegar based marinaded bbq chicken that made them famous.
This looks like an easy project on a much smaller scale..
Humphrey's DownEast Beast W/BBQ Guru