Ok, first up, I cheated! Yes I know I should have collected the stickers and added them over the course of time, but instead I bought a pre-printed vinyl sheet from eBay and "sticker bombed" my interior the lazy way. Having said that, it has come out great, and added a nice bit of colour to the otherwise dull grey/black carpet in the back of the van.
So the first thing I sticker bombed was the doors to the kitchen unit. To do this I took the doors off the unit and applied the sheet in the garage. I cut the sticker bomb sheet slightly larger than I needed so I could wrap around the edges.
Here's the sticker bomb sheet I bought:
Then applied it in one corner of the door, and spread it out evenly, making sure there were no bubbles. Then I shaped the corners and wrapped the sheet around the door edges. Finally I applied a small amount of heat with a hair-dryer to shrink the vinyl slightly to ensure a good tight fit. The result was awesome.
The second part of the interior I sticker bombed was the plastic supports between the roof panels. Again I removed these from the van, and applied the sticker bomb sheet in the comfort of my garage. Again, the result was awesome.
Take a look through the pictures to see how I did it, and the end results.