When we got our Renault Master it was a standard panel van with no windows in the back.
As part of our conversion we wanted to add windows to the living area. We chose to add them just behind the driver’s seat and on the sliding door. There are loads of kinds of campervan windows, but we wanted some that actually fitted snugly on the Renault Master.
Our search took us to http://www.vanpimps.co.uk who seem to have windows for all kinds of vans. They had a pair that were specific to the Renault Master – they are kind of oversize windows so they fill the whole gap (see the picture below).
We took the van to a local bodyshop who cut the holes in the bodywork (you could do it yourself, and vanpimps have some good videos, we chose not to!) and bonded the new windows on. The result looks like this: