I've been lucky. I use multiple locks, including a security chain through both handles of my generator (it is a 3000 watt porker), combined with a tailgate hinge lock. That way, I don't come back to a truck lighter both a tailgate and a generator (here in TX, tailgates are very often stolen, since they cost $2000+ to replace, not to mention the repainting costs.)
So far, the worst I've had stolen was a leaf bag full of camp trash and "output" from my bag toilet. The thieves stealing that did a pretty good job of pulling by my truck, relieving it of the bags, then hauling out like they filched the Hope diamond.
The one thing I've learned by living in the city. If you can't cement it down, use bolts. If not bolts, security chains, if not security chains, cables, if not cables, wires. Then after locking it down, insure it. Otherwise, some tweaker will be enjoying their meth rock on your dime.