I'm currently building a Spring Run and (for a number of reasons) went with an internal strongback, but instead of a 2x4 I laminated three layers of 1/2 plywood for a 1.5x3.5 inch beam, extended at the ends on the outer layers to mount the end forms. The sawhorses are braced together with scrap lumber to form one braced structure. So far it's worked well--still nice and straight.

: I would like to get a couple opinions from builders that have tried the 2
: main
: strong back styles. 2X4 up the middle of the forms vs. the big long plywood
: box type.. pros and cons??????
: Tks Rick