Similar to RLS clips and wedges. Might try a few...
NEW Tile Leveling Spacer System 250 Clips + 50 Wedges - Flooring Level- Lippage | eBay - http://www.ebay.co.uk/itm/NEW-Tile-Leveling-Spacer-System-250-Clips-50-Wedges-Flooring-Level-Lippage-/162452767721?hash=item25d2f083e9:g:Y5gAAOSwdGFY33ll
Yes, depends on the van. Vivaro/Trafic vans don't have support fixings on the top of the side loader. Transit Connect's for example do. I have deadlocks fitted all round. If they want in, they will get in but will take much longer to achieve ;)