The ash and fire box idea is adopted from Kamado smoker.
All fresh air will enter coal from beneath, and all fresh air will contact coal for burning. This way there is no excess fresh air is introduced and in turn fuel efficiency will be high. If I build fire box by ceramic, you can do really high temperature grilling, or it is great for baking bread/pizza.
In a common UDS, if there are two levels of grill, you may find hard to reach lower level grill.
I like the idea of PBC, it is easy to reach meat. But PBC also wastes space.
In my skewer plus hook combination, you can use most vertical space.
You can do grilling by inserting small block of meat on the skewer directly.
Meat size may be 1". It is very popular in north west China.
For slow & low smoking, you can hang big block of meat by hook.
You can instert 2 or 3 hooks on one block of meat.
My question: why do not you add lining on UDS by ceramic clay mud. In China I can buy ceramic clay at $100 for 2000 lbs. Considering shipping cost, I can not sell to you guys.
You can build such an UDS by yourself.
You need to buy a 55 gal barrel. What is the price
I can supply you
22" support ring,
6 pieces of 20" long skewer, diameter 1/2", stainless steel.
12 pieces of hook, diameter 1/4" stainless steel
Ash & fire box, umbrella, connect pipe, made from stainless steel, fire box size diameter 10", height 4"
Digital Power drafter of DOG package, PID outlet, one probe, same as AUBER.
My supplying price is $250. free shipping to North American
You need only to weld 3 stops on the barrel, and drill a hole of 1".