Adding insulation is always good but you need to observe your relative humidity and keep it at a manageable level, if the added insulation starts collecting water it may make matters worse. The difficulty is applying a proper vapor barrier to prevent moisture from getting into the insulation. FYI., the insulation should be applied on the cold side. IMO, taking showers and cooking with the vents closed and sealed and having a dehumidifier deal with the moisture is much more efficient than letting cold air in that causes condensation, don't worry about suffocating no RV is airtight. We live in our trailer where the temperature drops to -40C and trust me you don't want any window or vent open, not even a hair.
Here is the link to a current thread discussing a similar issue.