How Important is Double Pane Windows? (Precept 3UL & others)

Our entry level Palazzo has standard dual pane windows. We owned a different coach and it had single pane windows. It was very difficult to heat and cool. We also ran a mechanical dehumidifier 24x7 to keep the condensation down. It was a major nuisance. We even had to run the generator and roof A/C when driving on occasion because the dash A/C couldn't keep up.