Caravanners run generators themselves, big generators can be pretty quiet and possibly sound proofed a bit away from the the site.
The other option is as you say off grid possibly with Solar panels for some electric.
I'd worry a 5 van caravan site wouldn't pay for a large silent generator etc, if it was for something like clamping pods then would be more viable .
If you started with a solar system or similar you could see how it went before deciding to spend the big bucks