Van deadlocks are available for most vans these days, they look neat and can be supplied keyed alike to make it easier to get the right key, the fitted price for these deadlocks is £120 per lock

 Here is the Limpet MK3 Lock, now available after disappearing for a while It is simple to fit  and comes with a paper template so everything lines up. The two surfaces involved  need to be flush to within 5mm of each other for satisfactory operation.  An option of locks keyed alike is useful for vehicles using two or more limpet locks.