Hi Colin,
my advice would be to leave it on your van NEVER.
Trust me when i say this, but if you leave it on your van you are not only asking for the pole to be nicked, they could well know where you live and know you will have to replace it and have others.
They will sell them no trouble, so never leave it on the van, even if you could lock it in a pole tube.
You are asking for trouble.