An obvious one, but lock your doors, most crime that is committed is opportunistic. Potential offenders will walk past vehicles give the handle a quick pull to see if it open, so make sure you lock up every time you leave the van. Keep everything valuable out of sight. Park somewhere safe, choose a space that has maximum lighting with CCTV if possible. All these tips are fairly obvious but is it surprising how often we forget.
It is important to get the correct insurance for your van. Ensure that the van contents is covered by your insurance policy. Take photographs and keep a list of your contents, if the worst happens it will be easier to make a claim against your policy