Be VERY careful when re-tightening all of the screws that clamp the two halves together, the plastic lugs are very thin and they go brittle after a while and its VERY easy to give them the last little tweak and SNAP !!!
If it was me I would be thinking of paying a workshop, that way the worry is someone elses, and if it doesnt re-seal its not you who has to have another try !!!
(been there, done that, learnt me lesson the hard way. A new rooflight is EXPENSIVE !!)
Its not the destination that matters.
It's who you share the journey with (even if like me, itís in a caravan!)
I am very fortunate to have Mrs Plodd to share mine with
They do van conversions, and all types of repairs, and they really do the job properly, taking photos at each stage. They build up the corrugations in the roof, using plastic strip, to create a completely flat surface on which to mount the rooflight. This is the only way to make a permanent seal, so you'd think Adria would do this, but they don't.
Of course, MPI campers may be too far from you, you don't say where you live. But a good van conversion workshop like them should be able to help, or you could attempt the job yourself.