Many years ago I used to service and repair transport refrigeration units on trucks, when the smell got really bad the best way to kill the bacteria that live on the outside of the evaporator (the inside bit) was to put a steel dustbin on a pallet and fill it with screwed up paper and set fire to it.
Close the doors and wait for half an hour or so, as long as some of the paper was left unburnt then the fire had depleted the oxygen in the truck body to a level that would kill the bacteria.
I’m not suggesting that you try it in your van, if it was me I would use the aerosol on the floor type system cleaners as you will never get the foam to all of it.