Here is a sword heat treating forge I recently finished. It is 36" long and 16" high. It has one side arm venturi burner and 1" of 8lb inswool blanket lining.
For the body of the forge, I simply split a 36" long section of 8" pipe. Don't know where they use this type of pipe, but it's only 16 guage steel. I found it at the local steel yard. Then I just welded in 36" long by 8" panels on the sides. Some 8" by 16" panels for the front and back and a little reinforcing for the pivot points and I was in business. Just a basic frame to hold the works up. Did I mention the whole forge body rotates into a vertical position when not in use? Takes up a lot less space.
I added some wheels to the stand, on just the back legs to move it around and a digital pyrometer to keep an eye on the temperatures.
So far I've been able to maintain a good, even heat for most of the length of the forge and I'm very happy with it's performance. There is a little heat loss where the front and back openings are, as expected.
I got inspired for this design from forges I've seen done by Don Fogg and Daniel Gentile on Don's forums. There's a link to Don's forums and sight on my links page.