I think that if you look, your generator is likely already mounted on rubber mounts, so you likely won't be able to do much about any vibration that is transferred into your rig (watch your generator as it starts; it likely is shaking all over the place on those mounts until it settles down running). Depending on room in the generator compartment, additional sound-muffling material might help a bit with the noise. I've also heard that laying a piece of carpet on the ground underneath the generator can help with the noise.
