My Gen is also under the slide and the exhaust comes out under there near the slide corner also.
In 3 years we have had the issue about 3-4 times. Seem to depend on the wind mostly (or lack of).
The last time was one morning a few weeks ago at the Talladega racetrack campground. THere are lots of Gens being run there.
One morning, the exhaust smell was strong. I looked out over the campground and could see there was no wind and each RV exhaust fumes were just hanging over their own RV like a cloud. I also walked outside and the smell was strong just standing out there.