rustproofing 4WD

Vigilance.
before you go to beach
Wash and polish paint work.
Tectyl all the door panel internals, guards,sills, lift windscreen and windows seals and spray under there as well. Clean out all door and panel drains.
Thouroughly clean the under surface of the vechicle, touch up any areas that have bare metal, spray tectyl or lanolin over/into everything.
Do it all again immediately AFTER you come off the beach and a week later when the sand gland has regurgitated all the sand you missed the first time.
You could also try one of the electronic protection systems, but you'll still have to do the rest especially if youre into the salt water up to wheel hub height.

Just came across a write-up in 4wd action magazine (#127) for
using a DIY electronic rustproofing kit available form www.couplertec.com.au in Qld. I presume its similar to rustproofing used on jettys pylons etc.

It uses a tiny trickle from the battery to maintain a small negative charge on all body panels using capacitative coupling. which stops most corrosion.

Apparently cheapish (~$500 for DIY kit) and no harder to install than a couple of spotties.

Buy 2 cans of RP7/CRC and spray everything underneath when you get back from the beach . Dont hose it off . Wait until the exhaust is cold first before using . Do this everytime you go to the beach .

Chris,
In all seriousness, have you considered buying an old vehicle (Toyota fj45, Nissan G60, or even an old Landrover) to run the beach and/or launch the boat.

Obviously this is not an option if you have to tow for miles (sorry kilometres) to get to the beach from where you live.

If that is the case, plenty of washing down and liberal applications of Lanoguard/RP7/DWF/CRC/WD7 will slow down the inevitable metal cancer.

A few years ago, when we had plenty of water available I used to park my vehicle above the sprinkler and give it a good half hour blast each end. It watered the lawn at the same time.
In today's climate that idea would be frowned upon as definitely non PC.

Disco.

A large jockey wheel (not solid) on the boat trailer, a bit of brute strength and a long tow rope and you can launch a boat up to 5 or more meters without getting the vehicle near the water. Just unhook the trailer from the vehicle and manually wheel it in to the water for launching and recovery. Tow the boat/trailer out to dry sand with a long rope when recovering the boat, then hook the trailer back onto the vehcile.

We have done this hundreds of times with a 5m heavy as fibreglass boat with no problems and the vehicle never goes near the water.

Stevesub