I had the same problem and opened up the exhaust side of the air discharge(it wasn't cut big enough on the original install) and installed the baffle or separator to separate the intake air from exhaust air.
I can now run the generator for hours at a time without it overheating.
I can post pictures later if anyone is interested.
The arrows show how the air was flowing directly from the exhaust side to the intake side causing the generator to over heat.
The baffle I added directs the exhaust air to blow down further so as not to get drawn into the intake side.
The area marked with a square box was the part of the floor that I removed.