Lots of people have used plastic pipe. There are different types of plastic and some tolerate cold temps and impact. I like your idea of steel pipe. It would be more durable than the best plastic pipe and it would be easy to add a couple tabs on the back side to be able to temporarily chain or bolt it to the blade.
It would be nice to do slight upward bends at the ends so it isn't as likely to dig in there. Maybe with schedule 40 there would be enough material to grind a radius at the end. We have conduit benders at work that would work great to tweak the ends up before cutting a slot for the blade to rest in. For that matter, with steel pipe it may be easy to add tabs and just bolt it on without slitting it.