Mathesonandrew, i know this wont fix the desire to do this all yourself, as i also wanted to do, but i figured for the time i took to figure this out on a site that needed to go live ASAP, it was easier to spend $29 and purchase the WooCommerce Tab Manager. I can confirm it works perfectly and gives you so many more options - you will be up and running in 5 minutes!
I would still like to see a working solution to this once figured out though, for my own curiosity!