: Would joining 2 2 x 4 x 10' boards for a night heron strongback (13' 11"
: I believe) be realistic or effective? If so how should one go about this,
: I'd appreciate your comments.

Forget the 2 x 4's!!! What you need is a good, stiff strongback, and the only way to get it is with a deep section, like one made up of plywood in a box or "H" section, and since the box section is so easy to make, that is the way to go. You can usually find damaged 3/4" plywood at a Home Depot or Lowe's that is marked way down, since you are going to cut it into long strips, you can use the undamaged portions. You can even get them to cut it into the right widths for you if you have the dimensions before you go in to buy. ---
good luck!