I don't know how it would work for genny's, but I know a method that works great on ball mills. Ball mills have a running 3/4 HP electric motor and a bunch of lead balls tumbling all over themselves. It's loud and annoying.
We make the boxes out of thin plywood to encase the mill, then line them with ceiling tile. They don't call it acoustical tile for nothing! I've tried duct board too, and that worked pretty well, but nothing beat acoustical ceiling tile. That, coupled with a long heavy extension cord should do the trick. In Florida, so you know, some days it's mid-nineties here in the spring time.
I have a buddy who is the classic don't-give-a-damn-about-anyone-else RV'er. He cranks a noisy 6500 up every morning at 7 to turn on the AC and make coffee.... I may make a box for his and see how it works :-) We're not camping sans shore-power till next spring again though, so maybe this thread will be twice as old .
