With the unusually cold weather and high humidity here in the Texas Hill Country this winter I've experienced evidence of condensation on my cargo doors and main entry door as well..., especially with the furnace running (LP adds moisture).
Not aware of any 'coating' that can be applied to eliminate condensation...., best thing is reducing the humidity level inside the RV and/or air flow ventilation.
I'm presently wintering in Texas and use a small dehumidifier along with a couple containers of DampRid in my storage areas during cold weather and/or high humidity conditions.
Back in Michigan I place a couple containers of DampRid inside my TT when in storage and leave closet/cabinet doors slightly ajar.
Bob
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2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)