I have used the foam ear plugs in the past and have had some success; depended on how fatigued I was.
Also, the extra battery is an option; The E450 supposedly has a chassis location to mount one near the V10 under the forward right side of the chassis. Designed for a second engine battery, but could be wired to run the DC fan circuit. The long wire run would probably require a larger gage to insure minimum voltage drop when powering the fan.
The A/C noise is more of an "air movement" noise and for me, not as annoying as the generator.
I checked the link provided by Joe for soundproof cow.com. That product includes a liquid material to coat structures and absorbs noise and vibration. I might coat the outer shell of the generator and see if that helps.
