[Blueeyedfrog]

Thanks everyone for your answers.

If I'm not mistaken, blanket insulation appears to be cheaper than the more rigid sheets. In order to save costs would it be a good idea to use sheeting across the corner and fill the space behind with the cheaper blanket filling. Or would the blanket compress too much under its own weight? Unless you could use vertical runs (stand the insulation on end rather than stacking wedges on top of each other as done here) and glue them together to reduce sagging?

Cheers,
Blue