It might take a bit of work, but get this trick right and you're going to look pretty steezy!
Firstly, make sure that you jump off something big enough to make sure that the ends of your skis get over the rail
Time your descent so that you land centrally on the rail which will help make sure that you are balanced. Towards the end of the rail is where it gets interesting, as this is where you throw in the blindside 270 off. To do this use the edge of your lead ski to dig into the edge of the box so you’ve got some grip for your spin off.
The landing is all about timing, as you need to get the 270 degree rotation round ready for the landing. There’s a risk of over or under rotation, but with a little practice you will soon be able to comfortably build this into the trick.