There is a place at Colwick on Private Road No7 that fitted windows for the Central Vanz and Trux franchise. I can't remember the name but they are immediately on the left in a big shed building as you turn onto the road.
If you use the postcode NG4 2JW it will take you there.
I saw some bonded windows they had fitted in a T5 and they looked OK.
They do all sorts of conversions, horse lorries, campers etc.