Hi Fred,
Welcome to the Heartland Owners Forum. You'll find lots of useful information here along with a bunch of friendly and helpful people.
We spend 4-6 weeks in the Colorado mountains for ski season each year with temps as low as -30(F). We're happy with the dual pane windows and don't get a lot of frost buildup.
The actual improvement in insulation value is not the same as in residential windows, where there's inert gas or vacuum separating the panes. Nevertheless, they do help in summer and winter, and also cut noise. The large windows in our RVs provide a very large area for heat transfer - in during the summer, and out during the winter.
From past discussions on this topic, I would say that most owners who opted for dual pane windows would not go back.