I just completed this hatch strut R&R. The two most difficult parts were getting the rear strut pin in and folding the window rubber back over the plastic headliner. For the strut pin, I slid the strut back and inserted it first from the inside. The I twisted the strut and slid the pin out a bit just enough to get the end around the hatch holes. Then I used a small screwdriver to push the pin in from the side. This took a few attempts so can be frustrating. Take your time and take a short break of you need to. Another guy posted using a hemostat (thin pliers). Sounds like a good idea but I didn't have them.
For the rubber, get a thick coat hanger, cut it and make a small "U" at the end. Then use needle nose plyer to grab it before the headliner. Once you get the "U" part of the coat hanger under the lip, work your way down from front to back. Slide the coat hanger down a few mm and then twist it a little. Repeat this as many times needed to slide it all the way down from front to back to cover the entire lip of the headiner. It CAN be done.
Now I just need to get the small plastic fasteners for the plastic cover at the top of the hatch. They seem to fall off eventually, though. Maybe MB should have used small screws like for the headliner over the struts.