Fogged up dual pane RV windows were a common problem with coaches of about that vintage. Do a web search for "fogged RV window repairs" and you'll find multiple businesses that can repair your existing window for you.
Jay & Peggy Monroe with Dolly
Can't take it with you - don't plan on leaving any behind
2016 Newmar London Aire 4553, Spartan chassis
2020 Jeep Wrangler toad