The other thing we have done in a campground is to put our generator in a big translucent plastic box, with old towels all around it. The box is prominently labelled "dirty laundry" and it goes under the trailer, along with our other boxes of wood blocks and sewer equipment. Hopefully, if the thieves are (1) fastidious, (2) literate, and (3) gullible, they will be repelled by the thought of touching our laundry.
Or maybe they will just dissolve in helpless laughter at our feeble trick, and they will be too weak to pick up the heavy generator. Either way, it works.