Creating GoPostal missions but got a issue with spawning the van

Am looking for some help and information what am trying to do is spawn the GoPostal van only for quests but the code below keeps spawning random vans I like to know how to stop this also I like to know is there away to limit the number of vans a person has with out a database ?

         local numberHash = -119658072 -- GoPostal van
         local myPed = GetPlayerPed(-1)
         -- local plate = math.random(100, 900)
         local spawned_car = CreateVehicle(numberHash, -319.4503, -1024.8765, 30.0651, true, false)
         SetVehicleOnGroundProperly(spawned_car)
         SetVehicleNumberPlateText(spawned_car, "SeedlessRP") -- maybe get plate from database
         -- SetPedIntoVehicle(myPed, spawned_car, - 1) -- sit me in the van
         ShowNotification( "Your GoPostal vehicle has arrived." )

Thanks