Strangely enough i don't. The reason is i don't worry about anyone running up the road with a 650ltr tank of water
The biggest value is my poles - hard to pinch when i'm using them and difficult to steal from my van when it's backed up to my garage. However, it would be very wise to take out insurance but read the stipulations first on your cover. You will probably find you need an approved alarm and/or deadlocks to the van doors and you will not be covered if the van is unlocked (obviously)