A scoop would work great. I also saw references to using automotive radiator fans (electric) which would probably do the job also...
I've got a 13 year old coach, so my guess is that maybe my 13-year old fuel pump is starting to get weak under heat. Regardless, I'm not yet willing to go in and start rigging in modifications like this just yet... Honestly, I'd probably go to another Onan more suited for heat.
The other thing we haven't tried is pulling the covers from the generator and making sure nothing has built homes on the fins... Add that to my to-do list.
I have, however, found several people with Marquis 5500s that have the same overheating issue.