A lot depends on the campground... My wife and I tend to stay at membership campgrounds... At one of them there is one main entrance, it has a guard shack, and it's about a half mile from the shack to the first campsite. Though I do lock up my bike I do not anticipate any problems.
At another, a state park, where you can see the campers as you drive by,,, Well we got up one morning and found we'd lost our breakfast... Now many campers have lost their breakfast but it would have been nice if we'd had a chance to eat it first. They also took lunch and dinner (and the cooler) Others there lost medications, chairs and a grill (We did not loose any of that) Of course there is no security there.
Campers, at least the kind we (meaning forum members) tend to hang out with, are generally respectable However the people who drive past the campground may not be quite so nice. From what the deputies could gather in the case above it was some local punks who came by to raid the campground, they were not staying there.
Of course it appears a couple of punks came into the garage at my other house and cleaned out everything they felt was of value too, including 2 generators, a table saw and some other hardware. So even houses are not all that secure (And that house is in a very good neighborhood)