Just bought a nymph kit, and don't underst and how the strongback goes together from the pieces contained in the kit. Does anyone have a diagram of a cross section of how to assemble them? I know that I must be really dense not to figure it out, but it has me at a loss. I thought that it was supposed to be a closed 4 sided box beam, but the part sent can't come out as a square box I don't think. Thanks for any help.