The author's name slips me,but if you look at the drawings for camp furniture in "The Prarie Traveler" (1858 or 59),there is a bed that is much like the canvas bed with head/foot board you described.The head and foot board were used as both the legs and also used to hold the canvas mattress up off the ground.The mattress was held in place by simply inserting the poles through a small slot and putting a peg in place.I will look up the description tommorrow at work during my down time for more details.Hope this helps.
South Union Guard
"Always carry a flagon of whiskey in case of snakebite, and furthermore always carry a small snake"~W.C. Fields
"When I drink whiskey, I drink whiskey; and when I drink water, I drink water."~Michaleen Flynn 'The Quiet Man'