I've found different vans need different glues!  Some metal seems to be more sticky than others... For most I think the evostick contact adhesive will work, but I've heard some folk say that didn't work for them.  There is an industrial glue that the professionals use, but as far as I know you can only get it in bulk.  So, Trial and error unfortunately!  If you have any revelations or find the perfect solution, please let us know!!