We not only have MaxxAir's over our two vents and keep them open about half way all year round when the RV is in storage in the backyard ... we also keep the thermostatically controlled Fantastic fan in the front vent set to around 80 degrees. In hot weather this comes on and pulls outside air through the entire length of the RV to help keep the interior temperature down so that excessive heat buildup doesn't slowly ruin things over time.
Our RV is plugged in all the time when in storage, so we also keep an electric heater inside turned to come on at around a low of 50 degrees. This stops freezing during winter cold snaps, plus helps keep mold from forming due to the damp air during cold fall/winter/spring rains.
The interior of your RV should be maintained the same way as you would maintain the interior of your residence ... never too hot, never too cold, and never too moist.