We carry our Honda 2000i in an aluminum tool box which is mounted at the front of the truck bed, in front of our fifth wheel hitch. There are no issues with fumes. I was concerned that the generator might get hot when inside the unventilated tool box in the sun, but it always feels cooler inside the tool box than anything outside the tool box in the sun.
We used to carry it in the front basement of the fifth wheel, but while the generator didn't have gasoline fumes, it sure did smell like the inside of a muffler.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch