I bought SSD for my macbook pro 13" and another mabook pro 15", Also, I put more other Hard Drives for my data via "data doubler" from OWC too. Now I have DVD-Writer outside. That is why I buy "9.5 mm Optical Bay SATA Hard Drive Enclosure". It helps sometimes when I need Optical Drive again.
Firstly, I open 8 crews off from my mabook pro 13", then put the back panel out of the laptop.
Secondly, slowly put out some cable on top optical drive. also, open 3 crews keeping optical drive.
Thirdly, put data double including new hard drive in optical bay, then close 3 crews back.
fourthly, open the 9.5 mm Optical Bay SATA Hard Drive Enclosure box, take enclosure outside. Silde to open the closure and put dvd writer in.
All done!!! I think it is very easy to do ourselves.
Every step to do in macbook, try to do gentle because of it is very easy to brake or bend.