I have been considering a 2 X 4 strongback made of plywood, a 2 X 4 inch aluminum extrusion and schedule 40 plastic pipe.

The 2 X 4 plywood is pretty straightforward and inexpensive. It would not take too long to make--maybe a couple hours. Some care has to be done to make sure it is straight.

The aluminum extrusion is straight and ridgid, but will probably approach $200. If anyone used a 2 X 4 rectangular extrusion, let me know your experience. If other than 2 X 4 extrusion is suggested, I would like to hear your experience.

I have heard of people using schedule 40 drain pipe (4"?) as a strongback. It would seem to be a good idea. It is quite ridgid, VERY cheap (less than $10 for a 10 ft section). I am not sure the best way to attach the forms, but it does not seem like it would be a big deal. The 4 inch sched. 40 is a little over 4 inches in diameter and would require some modification to the strongback dimensions in any plans I bought. If anyone used schedule 40 as a strongback, I would be interested in their thoughts on how it was modified to attache the forms and stem pieces, if 3 or 4 inch was used and any other feedback.