Not sure which vent you have, but this one fits many RV vents:
https://www.amazon.com/Slide-Co-2225.../dp/B000CSN4LC
This is another option for longer reach:
https://www.amazon.com/SureReach-Kno.../dp/B08Q4C8X9N
Another, DIY option I've seen suggested elsewhere is to cut a piece of PVC pipe to the length you need and then cut slot(s) in one end to fit the existing vent handle. For the round twist knobs, that would need a large diameter pipe with multiple slots cut in the end. For the crank handle type, I think you could make a smaller diameter pipe with a single slot cut out work. You could put a T on the handle end to make it easier to use. You wouldn't leave it attached, just store it in a drawer until you need it.