1. Covers for the fridge vents which some people put on over the winter months, these should be easy enough to spot as they will be clipped to the outside of the van in line with where the fridge sits. I've never used them.
2. Heating. Our van has a vent outside that has a clip on/off over over it which must be removed if operating the water heating by means of gas (but it is left in place if using 240v)
Everything else I can think of externally is a flap rather than a vent cover.
Hope this helps a bit, I'm sure other will be along with more suggestions though.
** EDIT - Which make/model of van is it?
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Just bought and fitted vent covers for the fridge on my sport, they weren't supplied. Here
are the vents(grills) and covers. Solid bits are the covers, slotted are the vents. So if you can see the slotted areas fully then covers not fitted
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