at the risk of getting "Booted". like on the other trailer forum.
replace the muffler.... from a Honda lawn Tractor. like the 4514... e-bay used.
install rubber engine mounts .. as the frame is a mechanical sound amplifier.
overhead valve engines are LESS noisy then flat head engines....
and ADJUST the valves.... most come from the factory very LOOSE...
NO it will never be close to an inverter type.. but things can be done to lessen the noise...
and can save 400 plus dollars..
not everyone can afford a high price inverter-generator. for 2 to 10 hours a year...
I use my modified construction generator for 3 hours per over 3 days.. twice a year...
I dry camp.. and NO ONE IS AROUND...
2 hours in the evening and 1 hour in the morning.
so 18 hours per YEAR...