Option C) Electrical Box install 2 of 3.

If option C) was your Electrical Box choice, you wouldn't need the 1" Sheetrock screws shown in the photo (used to hold option B) battery in position).
You also wouldn't need the aft upright 2 x 3 to be so tall, or need a 15 degree (off 90 degree) cut on both 2 x 3 uprights. Both upright 2 x 3s only need to be cut 1" longer than the top of the 2 x 6 swing-arm, and only at a 90 degree angle.

Y11-09-17