Originally Posted by nashrover
I suspect this is moisture that has somehow breached the weatherproofing.
Do you have a second skylight that is clear or are you just guessing? Two trailers that are exactly the same sounds like a design feature rather than a coincidence. Similar to the OP, our skylight is perfectly "frosted" rather than randomly exposed to the elements. I've actually suspected that there was a factory protective film that wasn't properly removed before we took possession.