I thought it was interesting too. A few of the carts out their look pretty inefficient. I would be worried about piling on wood and losing temperature.
I actually have my deck oven (easily converted to propane) on my trailer now, and when I asked a friend for help in moving it OFF the trailer, he said why don't you just leave it on their and go do some festivals? I think the thing is it is not as easy as you would think to get into these. I might have to start by showing up somewhere and GIVING pizza away for free!!! I guess the wood burning makes it more interesting, though.