Buzz,
There are several different soundproofing materials on the market.
Cut to suit & adhere with adhesive. Look online & there's a plethora of info. You will find what you want locally.
That being said, one drawback to insulating is not being able to hear any change in engine sound, water leak spraying, bad engine mounts etc.
I have a keen hearing sense & always know how something running normal is supposed to sound. If a familiar sound changes slightly, that's the time to check it out.
While soundproofing is nice, there is a trade-off. I was going to put insulation in awhile back but, after thinking about the, "what are the drawbacks", I decided not to.
Depending on you compartment configuration, you may be able to insulate the noise areas like covers & access areas & not the entire compartment.
CR
