In reply to the ant hill mob:
I have a LWB Sprinter, I got it converted by a conversion company but from what I understand the thickness of the sky light depends on how much insulation etc you have, as the measurement goes from the outer skin (van roof) to the inside of the lining (the ceiling inside the van). The top half of the sky light slots in from the outside the bottom half slots in from the inside and then they are screwed together to pull the outside bit closer to the roof and make getting a seal easier, but the sprinter roofs have ridges running length ways along them so this makes getting a seal quite difficult (mine leaked this winter and I had to get it re-done).
Hope that helps?
