You are getting the hang of it. Just imagine your van is basically a tent with more solid walls and roof, and is on wheels and you have the picture security wise.
However, do not be too disheartened. The number of thefts from vans is relatively low and in Europe you would be amazed at the amount of quite valuable stuff people leave lying about in the open, and nobody touches anything.
The majority of thefts are looking for cash and credit cards. Therefore do not leave these in an obvious position.
Also note that if you have fitted extra locks then a thief may decide yours is the van to go for. It is a crazy world.