I intentionally didn’t include those washer gaskets in the instructional video because I don’t consider them part of the standard install. They are there in case anyone wants to experiment with a very soft build, but as you noted it’s quite tricky to get the torque on the screws right without tearing them. I’ve had success with it after a bit of fiddling, but it helps to not stress too much if it isn’t the most beautiful thing in the world but instead just gets the job done, as inevitably the washer will get a little deformed. My general advice is: don’t mess with it and just install the upper gasket. 
I haven’t really been able to tell much of a difference with those backing washers installed.