cooter
If you went with charcoal or coal for just a quickey forge
You could stack bricks around the flue and use a pipe to get the air in the fire
for the air supply you could use a hair dryer duct taped to the end of the pipe.
Just prop it on something so the pipe angles down in the fire.
This would be like a side draft- if it comes in from the bottom its a bottom draft.
this is a side draft
With gas forge you need to build a burner , insulted shell .
Glenn made a forge called the 55 Forge its a bottom draft (BP0133), and another that was side draft (BP0238). Any how easy to make.
You can use other things for flue some even use corn.
Don't use anything galvanized fume fever is bad news.