I needed to bend some wooden strips one time, so made a steam box out of PVC pipe and my wifes carpet steam cleaner. It didn’t work out well, the steam softened the plastic pipe and the whole thing collapsed. The next attempt was to use MDO plywood. That worked out a lot better.
I used steel spikes crosswise inside to create the rack to hold the pieces up so the steam was able to circulate all way around the strips of wood.
It maintained a 220°F temperature inside the box
The box worked great, the product not so well. I was too impatient and I guess I didn’t let the wood “cook” long enough and it broke while bending. I can not even remember what the project was, but figured out another way to do it. I think it was the back slats for a rocking chair I was repairing for a friend.
also forgot to mention that the box was on a slight angle to allow the condensate to drain back to the bottom end and drain out a small hole. There was also a small 3/8" hole in the top of the high end to allow the steam to travel all the way up the box and escape.