I have to add my two cents worth in agreement with some previous comments. The strongback does not need to be straight, it needs only to be stiff enough and stable enough to hold your forms accurately until the strips control the shape of your hull/deck. Internal or external does not matter, just do what you need to do to line the forms up properly. With your internal strongback, this may mean cutting the holes in your forms larger than they now are to make adjustment room. You will also want to run a string line longitudinally and place your lateral forms at right angles to the string line rather than to the bent lateral surface of the strongback - also, place your bow and stern forms parallel to the string line rather than the strongback.

I would not consider building another, it will likely end up less than perfect no matter how much you fuss with it. Again, straight does not matter. Stiff and stable enough does. Spend your time lining up your forms precisely, not building another strongback.

One final note on your internal strongback, if your current plans do not include them, I recommend temporary angle braces from your floor or support post to hold your bow and stern forms exactly centered until a couple rows of strips lock them in place, The internal strongback could have enough flex to cause mischief otherwise.

Good luck,

Allan Edie