I recently purchased one of MidNite`s pre-wired combiner boxes. I must say, pretty awesome and painless if your using MC4 connectors. I`m sure I paid a decent amount for it vs making my own but simplicity/ease of use got me this time.
I only have 2 strings so I used an open string to connect an existing MC4 (furthest right) cable to my inside connection. For me it was click click click done.... Painless and perfect.
Thanks MidNite and NAWS!^