Converting Single windows to Double Pane?

Hi--as a twenty year (and counting) full-timer who has spent many winters in our RVs in single digit temperatures over the years, I second the motion for either Plexiglas or window film instead of going to the trouble of trying to replace single-pane with double-pane windows. Having had both, I can tell you that the double-pain (pane) windows don't make that much difference. You still get much cold from the metal frames plus you have to deal with seal failures and window fogging with the double glazing. Save yourself the money and the aggrevation and insulate what you have. Stay warm!