[Patrick]

The series adapter looks right.
If you are only going to use it with two packs in series then you could get rid on the middle deans plug and a few inches of wire if you wanted. Just have the - esc wire going straight to the same spot on the left hand side plug, and the + esc wire going straight to the same spot on the right hand side plug. Probably move the adapter back to the next hole in the chassis since you'll have less wire.
You don't have to do that, it will work how it is, but it looks like your going for a neat layout so getting rid of a plug and some wire might make it neater (plus less overall resistance helps a bit). If your going to use single packs, or parallel packs as well then it's not worth doing.