5000W would be nice to have when on 50A. But number clarification: 50A service is 120/240V and 5000W would draw 21A on 240V so a 30A dual breaker would work. And the equivalent amps for 120V would be 42A which is not supported.
The next wattage I saw was over 3600W. What is that used for as it exceeds a 30A service? Below that was about 1800W which would be OK on 30A. And it shouldn't be used on 20A at the recommended sustained draw is 80 percent and electric heaters are in the sustained draw class.
It's a moot point for me as I don't have a propane heater and I do use up to 3 portable ceramic heaters.
208V is for 3 phase service and not available for RVs.