We don't have a problem with saggy roof on our freestyle, but we do get condensation in the front main light. I get a good couple of egg cups accumilate in the light fitting. I've leak tested the whole van outside and we can't replicate the situation. On dismantling the light fitting I noticed that the roof insulation is bonded to the inner liner but not the aluminium roof skin. The wiring for the roof lights lies on top of the insulation with potential for the roof skin to pressurise the wiring. So a heavy snow loading might be a fire risk if the wires were compromised.
I have concluded our condensation issue to be caused by towing the van on a cold day and having the van about 24deg C before towing, then as the van travels in sub zero, the aluminium skin attracts condensation to it's inside face, culminating in the moisture which only is apparent from the area above the axle forward, exiting via the only breach in the insulation at the front roof light. Had the aluminium skin been bonded to the insulation the moisture would be absorbed by the polystyrene. I have regularly checked the walls and roof with a damp meter and never find more than 20% moisture. Its a very strange event, but given that we fulltime, and use the cooker daily with a pressure cooker as well, steam has to go somewhere.
As a precaution, I'm going to seal the outside of the roof rails, two heki lights and two other vents with flexble silicone sealant. But given that the van has been fine in torential rain for days at a time while on site, I probably won't see any improvement. Short of stripping the outer roof skin and replacing it with a new one bonded to the insulation, there seems no posative solution.
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