Coachman VIP roof light leak

Hi 

Just wondered if anyone had experienced a water leaking in via the front opening roof light on a Coachman 575 VIP - 2018 model?

The van has been in storage a few week and I always leave it slightly higher at the front so the rainwater drains to the rear. Never had any problems until last week 

Loaded the van, no sign of any leak inside, hitched and drove approx 100 miles to Forest of Dean, no rain en route.

On arrival at the site pitched and opened the van up and found a wet carpet directly underneath the front roof light. Very strange, no signs around the frame of the roof light and still shut tight. 

Removed the centre covering trim of the roof light frame (inside) and found a small amount of water and slight drip, but minimal.

Had 5 days and nights of heavy rain and wind - No leak and no problem since.

I have asked my supplying dealer to check  (and add to other ongoing build issues) and at first, pop in and we will inspect, this has now changed to 'had this once before and but not happened since, but don't know what the cause was'?? Must be forced in while driving? If not leaking now don't worry

Surely the roof light should be watertight regardless of conditions

Been to Spain and the South West of France through torrential rain with no problems

Not accepting the dealers response and will persevere and get the van checked.

Has anyone experienced this issue and if so any ideas on the possible cause?

Many Thanks