2 alternative routes to Robertson - much of a muchness

*        Via Sutherland and Princes Highway is shorter but slower

*        along M5 and Hume H'way is longer but quicker

Princes Highway to Robertson Showground - via  - 124km from Harbour Bridge

Take roads twds Sydney Airport, but remain on Princes Highway heading to Sutherland and twds Wollongong.
After descending Mt Ousley, veer right a follow signs to Kiama/Nowra, remaining on Princes Highway.  Albion Park Rail is about 10km Nth of Kiama.  Veer right onto Illawarra Highway just before Albion Park.  Drive 10km to start of KOM Climb up Macquarie Pass, a further 12km to KOM of Macquarie Pass and a further 5m to Robertson Showground. 
Pick a camp site in a hollow 'cause they are lush, verdant and soft, and it never rains in the Southern Highlands, and assemble your trusty tent.

M5 and Hume H'way to Robertson Showground - 144km from Harbour Bridge

Take Eastern Distributor for 9.7km onto General Holmes Drive for 2.3km; OR

Lane Cove Rd / Homebush Bay Drive / Centenary Drive

*    SW on M5 Western Motorway for 21km,
*    Sth on Western H'way for 42km,

*    SW on Hume H'way for 25km;

*    Exit onto Old Hume Hwy 1.2km

*    Left into Aylmerton Rd for 1.2km

*    Right at Old South Rd for 6.7km

*    Left at Range Rd for 4.9km

*    Right at Ridge Rd for 3.2km

*    Right at Tourist Rd for 0.6km

*    Left at Kangaloon Rd for 0.9km

*    Ahead on Sheepwash Rd for 5.1km

*    Left at Illawarra Hwy for 11.3km