I've had my 2003 for 14 years and there are very few 4WDing scenarios that I haven't put mine through. Still has original paint on underbody and chassis. Apart from a bit of minor surface rust on the chassis and suspension components from stone chips underneath it is rust free. I have seen a 2000 GU wagon with major rust in the floor area though.

I like shiny stuff

 

!9 years, owned since new, been everywhere, including long regular beach drives, I don't wash the old Troll regularly but do flush underneath after every beach drive. She is in very good nick, I'm hanging onto her because there is absolutely no reason to do otherwise.

I have a friend with a slightly younger vehicle who does have rust though and does a lot of beach driving, I think how you handle it when you get it back home plays a role in keeping the rust at bay.

 

I have a 02 series 3 sitting in my backyard which I bought 3 months ago to swap all my GQ bits into. It came from mid NSW along the coast, bog stock, not an ounce of offroad dirt on it. However there is rust in the lower radiator support panel, which I put down to salt air being parked near a beach, a couple of 20c size patches which I need to attend to. A mate had to get his 2000 model support panel replaced it was that bad. From a little bit of research I've done I think this is a common spot for it, insufficient drain holes I read as a cause.

cheers.

 

So far reading posts I'm rather impressed with vehicle age before this rotten stuff sets in . I know the metals used these days are alot better but was just curious as they are 4x4s that cop alot of rough stuff . Thanks for the feed back peeps.

 

These only really rust where dirt collects especially once the paint is gone.
Worst places I've seen are:
The top of the front coil mounts, worse if the cover plate is left on.
The chassis/gear box cross member area.
Where the flares meet the skin.

My GQ wagon is scratched and chipped quite bad and been in the ocean more than once.
The only place I have had to remove rust was behind the passenger rear flare where one of the bolts trapped mud.
I very rarely wash it but do hose all the places that trap salt, sand and mud most times I come back from the beach.