Mal, sorry for the delay!
The next time in the USA I will put some stickers over the code from the rental car, that not everybody can see this is a rental car. I will rent a car without a knob in the panel to open the trunk. Someone told me, that many thief make a curve around black cars, because that maybe can be a car from the police... Don't know is that true. I will try to par on a parking with a parking attendant. And what I find a really good tip: When you put something in the trunk, don't park there. Drive away to the next street or so, that nobody can watch you and can see there is something in the trunk! And, I will place a small alarm in the Backpack, what reacts on shaking. Maybe have other peoples also good ideas how to secure it a bit more in the car! Oh, and sorry for my bad english! rem