You can try the medium cover but it will be big on the generator.
Dear RVnewb, My Generator sits on my porch. The cover fits good but I put a bungie cord around it since my first cover blew away with the high winds we had a while ago.
Yes, I have a Sportsman 4000 dual fuel, fits perfect.
If the generator is no more than 18 wide 22 long and 17.5 high. It should fit.