[rhagfo]

Originally Posted by sourdough

I agree that it's more than likely condensation but I would also check all the seams if that is possible. If you can't raise the vent covers I would get a "good" dehumidifier and run in both the living area of the trailer and in the shower when showering.

The MaxxAir covers are worth every penny. No snow buildup, rain intrusion etc. and you can raise the vent for humid air to escape at any time.

We run a HiSense dehumidifier 24 hours a day when it is humid. It's pretty large (50 pint? 35 pint? - don't remember) and it's amazing how much water comes out of the air. At times the bathroom will still get a very small amount of condensation on the ceiling when we shower if we forget to open the vent. If we do open it we have no issues at all.

Well I think Sourdough has hit the nail on the head!!
We full time and have vent covers, the last set were cheap Camco after four year they became brittle, lost the one over our bed in a strong wind storm.
Even with a dehumidifier running 24/7 I noticed light condensation on that vent before I got the cover replaced latter that week.
We keep our dehumidifier located under our kitchen table, all air flow vents are clear and not blocked at all, that is where it lives and works very well!
These conditions are on the Oregon Coast, so yes it is wet! Currently outside humidity is 98% and inside is 42%.
I will add bathroom vent gets opened and the fan is on during showers. We also replaced tiny fan with a Vortex fan, yes a Fantastic would be better and quieter, but the Vortex is installed from the inside, so can be installed easily in winter.