Defrost hoses.

[GMCPaul]

If they have the metal spiraled wire in them rotate them like your turning a screw to thread onto the heater box outlets, then sick them through top opening of dash, I know its a stretch but they'll stick through the top and rotate the round vent on and then form the other hose to the oblong shape and by wiggly it some you can get the metal spiral past the tabs designed to hold it on. I generally pry with the nubs of my fingernails on the last oblong one. About a 5 minute install using this method.
Paul @ GMCPauls