Never seen a flat van... explain to them the difference between calendared and cast vinyls as far as longevity. They are paying to NOT have to remove and replace the graphics in 2 years with the additional cost.
If they want to replace it in 2 years, IJ35C will work and apply well.
Anything going into that crease in the side (assuming GM or Ford van) will pop out if not done correctly, not sure if IJ35C would stick well in there or not... probably would with Primer94.