In the past I have just saved reasonable sized bits and used clothes pegs to clip it to the frame.
But if you do not have a lot just make a cheap movable frame from some old baton, staple the bubblewrap on it and just insulate part of the greenhouse.
Cheap bubblewrap, any furniture store will have skip loads they want to get rid off. It does not matter about the size of the bubbles.
But, saying all this, I have never been completely convinced it made a blind bit of difference.