Hello Paul,
To find out what your dealer will do to service your caravan, ask them.
You can then decide if you trust your dealer enough to respect your property or not.
If you leave your caravan full of everything, how quickly would you notice if some thing was missing, and how cold you prove it was the dealer (or one of thier staff) actually removed it. an do you realy want the hassle and discord that might ensue if you did have to try to pursue a claim.
I think it is probbaly good sence to remove all valuable items that might attract unwelcome fingers.