High Top condensation problem

[Rich Tea]

I visited my van (at the storage yard) and was surprised to see the roof lining had sagged and one of the lights had fallen out.

The problem appears to be a not so good DIY conversion and plenty of condensation, the inside of the high top was covered in drips (which had soaked the hardboard ceiling panel).

I'll just shed a little more light on the construction of my interior before I ask a few questions.

It's a Van high top, like the one they show in the dimensions section of the handbook. The original DIY convertor has bonded two rails (running front to back) to the corners, each side and bonded square pieces of wood to the roof here and there. To the rails is fitted the ceiling panel (Hard board) which is also bonded on to the wooded squares. Theres some loft insulation stuffed in there (but not much). The sides are similarly fitted out with insulation bonded to the high top sides and hard board panels between the rails and the van body. All the joints are fibre glass bonded.

I think one of my problems is that the two rails are fibre glassed to the hightop, so once the ceiling panel is fitted this area has no ventilation at all.

Obviously, the reason I know how it's put together is because I ripped it all down and need to start again, so I'm after some hints and tips how to go about this so I don't end up with the same problem.

I assume condensation is inevitable, so how can you stop it, or manage it? If I insulate the roof, will it still form in the cavity? Should the cavity be vented, like the attic at home (if so how)? If I can protect the ceiling from the dripping condensation, where would the water go? Would it run down the sides to the space between the high top and the van, how would it exit from this area?

There's quite a few threads which discuss how people went about converting their high tops, but mine seems to have been done similarly, so I'm not sure where to go next.

In short, how do the professionals do it, and how can I achieve this with a bit of DIY?

Thanks for taking the time to read this and for any suggestions.

Rich