If it looks like it's secured, that will address 95% of the problem. Most casual thieves will look for easy to steal items and pass by something that looks difficult.
You also benefit from owning an off brand. That's less desirable than the name brand generators...but even then not sure how big the market is for stolen small generators anyway.
Far more likely would be to steal the whole truck and then part it out...at a chop shop, they will have no issue cutting the generator free of just about anything you come up with.