I've a 2015 Spark 710 and did an internal a week ago. My first dropper install and it was pretty straightforward. I went 1x so I used the front derailleur port. You can use a small file to open up the access. I used a drill because I didn't have a file that small on hand. It's probably less than 5mm to drill. Just used the smallest bit and moved up till the cable could fit.
