I did it last year in a small motor home, 10k gravel, small pebbles but drive to conditions and no problems, advised not to use the road from the west, power at Fowlers bay is limited to about 1500 w so cant run 2 appliances at once
The two main roads into the Bay have gravel sections. The western approach has more than the eastern one. Both are fairly well maintained. That does not mean you can drive those sections at highway speeds. Just slow down to a reasonable speed (that may mean very slow on some sections) and you will get your van in there without damage. My soft-roader has been on both roads without damage.
__________________
PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.