Quietening a Honda EU2I even further - Is it possible?

People have done this, and they vent the soundproof box with a fan which can be run from the generator. Generous ventilation as you put it would also allow the sound to escape. When we purchased our Honda, my husband mentioned a box with a fan in the shop. The retailer said that it would invalidate the warranty. We found the unit acceptably quiet anyway, and have camped near other caravanners using the same and had to step outside to tell if they still had it running.

Motherhen

Several options you may consider before box.

20 metres of 240V cable works especially if you put the genny behind - trees, banks, cardboard ect to shield the diect sound

be careful with the box re cooling air in or cooling out - as stated above vents allow sound out as well as air in/out.

shielding the direct "noise" (ie line of sight) and REFLECTED noise is the secret as well as absorbing any noise emitted nosie where possible ie acoustic tiles etc.

However to box it you could have a larger inverted box over an upright box with exhaust and mountings through upright box. Have adequade insulation inside boxes with air agp should do the trick.

You can mount to upright box and have waterproof inverted box as lift off for refulling/ starting etc.

Look on the http://www.campertrailers.org/ On the tech tips site

My Outboard makes a huge amount of noise on the muffs but if I submerge the leg in a tank of water it's nice and quiet.
So with that theory run your exhaust in to a tank of water and that should quieten things down nicely.

Cheers.

Here you go, follow these instructions..

Sound Proofing a Generator - Everything you need to know