I have never understood the whole “back the van to the wall” idea. If somebody can break into the front, they can release the handbrake and push the van forward ? Even with a steering lock, it will go straight a few feet. I guess it depends if you can get through to the back from the drivers seat, in my van you could unless you were really fat !
I have travelled in France and generally took the bikes in the room, if that wasn’t feasible in the back of the van with a few locks to the fitted railing to slow them down. Park somewhere well lit with CCTV if you can.
Edit, a and I did disable the inner door handle for the van, so you couldn’t get out the back from the back, but if small enough can wriggle through to the front. This did happen more than once when I managed to lock myself in the back.