To build a steam box, obtain a 10 foot long section of a polyvinyl chloride pipe that is 4 inches in diameter, two end caps, a piece of garden hose, a boiling vessel and a camp stove. Make two holes a little smaller than the garden hose in the cover and one of the end caps, and insert the hose in the holes. Fill the water boiler with water, and place it over the camp stove.
Don't buy a pipe that has a solid wall to use as the steam box, as it is not going to hold the heat in sufficiently, buy a pipe with porous walls instead. You can use any metal container that can fit several gallons of water in it as a boiling vessel. However, if the container used to hold flammable materials, wash it thoroughly first. The holes for the garden hose have to be large enough for the hose to fit in them, but not large enough for air to be able to leak through the hole when the hose is inserted. When drilling the hole in the cap, make it close to the edge of the pipe.
Make sure that the caps aren't going to fall off the wide pipe. If you feel like they are, secure them in place with duct tape. Secure the steam box on a stiffening board, and set it up on a surface that is located higher than the boiling pot.