Not many SWB GVs here, zooks4life used to have one
viewtopic.php?f=4&t=12961but has upgraded to a diesel LWB
viewtopic.php?t=33254also read these threads
viewtopic.php?f=1&t=38670&hilit=NGVviewtopic.php?f=5&t=39588&hilit=NGVviewtopic.php?f=3&t=38657viewtopic.php?f=3&t=32209also check Youtube, lots of vids of GVs offroad
For light offroading they're pretty good, just drive it accordingly. Don't know much about the SWBs, with the LWBs try to get the second generation ones from late 2008 onward as they get the better petrol motors, 2.4 4cyl and 3.2 6, early petrol base models also missed out on traction control, the diesels stayed pretty much the same apart from better brakes and slightly different interior.
Maybe consider the earlier GVs, pre 2005. $6-8,000 gets you comfortable car that's a bit better offroad than the newer ones, insurance should be cheaper too.