I have made my strongback out of 2 pieces of aluminum stud material - they both cost around $10. They are "U" shaped and I have them nested one inside the other to make a square tube. They are screwed to each other with pan head sheet metal screws. I don't have forms hung on them yet but I have pushed down on them fairly severely and don't see much deflection.

I have cut my forms with enough "wiggle room" to get past the heads of the screws. I'll align them like Nick shows in his book.

I haven't seen any problems with them yet.

Carl