I went in search of 12mm plywood (half inch) this afternoon and came up empty handed. I've seen various threads that warn against using MDF as strongback material. Then again I think it balanced out as there were just as many for using MDF as those against. My aim was to build the strongback according to Nicks book. Then it struck me I've got a few 2X4s that are 8 feet in length. I haven't found a thread yet that asks the question about scarfing two 2x4s to get the proper length. I can only imagine not getting it straight but I am willing to try. How much stress will there actually be if it were half lengths scarfed together and supported in the middle? The 2X4s that I have are just that 2" by 4" so I'll have to cut to fit the forms. I'm still considering the MDF option as it's so readily available.

Cheers
Jeff