Drill a small hole three to six inches up the pipe and then cut from that down to the end of the pipe - that will increase the resistance to the cut propogating further along the pipe. Fit onto the metal stubs with the drilled hole and slit on the inside facing side. Strap round tight once in place - cable ties and a bit of grunt to get them really tightly fastened.
Additionally, best if you can warm the plastic up too before stretching it over the metal.