border track

John, the SA / Vic Border Tk ?
If so, it depends what part as you can do it from the Murray R at Customs House, right through a fair way south of Serviceton.
The only part where it is wise to carry and use a sand flag is south of the one way section (2 way traffic starts at Centre Tk) to the road out at Pine Rd North.
Even on the one way section, probably best to run it too, as some vehicles, maybe you too, might use the bypass tracks in places to come around for another go at some dunes.
Other than that, once you head past the main dunes south of Red Bluff, you can just run headlights for visibility with the 2 way traffic.
A flag will very likely get some tree action though, loads of scrub encroaching . . . if this is an issue, just take it down and run the lights, crest slowly, and keep a sharp lookout, scan UHF (ch 10 is the official parks ch).

9 days ago we entered 4 kms before Pinnaroo on the Adelaide side (Rosy Pine Rd) or something like that. We picked up the border track from that road. One of the dunes along the one way section was quite hard to get up because it was as soft as beach sand and had almost knee deep ruts with quite deep offset holes near the top. Probably a headache for towing a trailer but it was only that one so live on the edge and have a go.
When we got to the two way part there were one way tracks over the dunes and some even had rubber matting for traction. A sand flag didn't seem required.
We were driving our wives cars for a laugh (Prados and FJ Cruisers) so didn't really know how to drive them well but we were worried about the twig strength front drive shafts so we were quite scared to break those dainty little shopping trolleys.
No extra fuel required.