Hey Buddy, welcome to the site. My friends use Dynamat in their cars and it helps a great deal. I don't know how your genset is configured, but on mine they cut a hole under the trailer below the gen. to allow air flow in. Not only is that the air intake, a lot of sound comes out of there as well. I put an exhaust extention on the pipe that carries the exhaust and some of the noise over the top of the trailer, but since a majority of the sound I am hearing comes out of the bottom, there is no much I can do to quiet it any more. It works great for the exhaust.
I tought about some type of sound absorbing material but my compartment is so small I would have to remove the gen. to install it. After thinking about all the work that was involved I figgered the sound was not all that bad and I could put up with it. If you end up doing it, let us know how it works.
02 F250 SD Diesel 4x4, 6.5 lift, Banks ex, K&N, Edge progrmr