We have a Northern Lights 5KW with factory*sound shield installed in a crowded lazarette.* The deck over the unit is fiberglass/balsa core and teak decking.
As an experiment, I took decibel measurements with the sound shield in place, and with it removed.* In our installation, the difference was 1 db(a) louder without the shield.
Even though most service points are available on one side of the generator, the shield makes access very difficult, and in fact blocks access to the fresh water tank valves*in addition to making servicing the steering system very difficult.
So, have removed the sound shield and will install 1/2" plywood faced with foam/barrier soundproofing on three sides of the generator.* Access to the generator and non-generator systems will be drastically improved, I don't anticipate any meaningful increase in sound level.