Agree re dynamat, good stuff
It is important to factor in air circulation for cooling, especially if your gen is air cooled, when packing/placing the absorbant material around the gen housing.
Putting a noise absorbing mat under the gen, direct on concrete or asphalt, helps, as do acoustic barriers to deflect/redirect and absorb noise.
Suggest you get a DB meter or an acoustic measuring App for a smart phone and experiment by measuring DB levels from fixed positions with different acoustic absorption materials and other noise abating measures in place. My free android "Noise Meter" app works great and tracks with my stand alone DB meter. It is much better to have some empirical data from which to base decisions.
Start by setting up a test plan, such as identify monitoring locations and measure without doing any abatement action and then record the effect for each time you put an noise reduction feature in place. It will be generally a trial and error method until you reach an optimum fix.
It is also a Good idea to measure temperatures around the gen as you apply the various acoustic dampening materials closer to the engine or air passageways.
The effect of Gen noise can be reduced markedly by the carefull positioning of absorbant materials and baffles.
Additional exhaust redirecting and mufflers also help. (But caution on the mufflers that put too much back pressure which could reduce the gen power, increase fuel consumption, and cause premature gen failure.)
Good luck, you can reduce the ambient DB level footprint markedly with well thought out and applied noise dampening techniques.