As for caring for your vehicle, the biggest offender IMO formed over the 45 years of owning old cars is mud.
It comes in 2 main forms, the obvious from off-roading or even driving up the lane after a tractor has dumped a load of it from the fields, or from a gradual build-up of dirt from the road which will happen to any car even if it never goes off-road.
Everyone seems hell-bent on washing their cars and trucks and getting a shine on the paintwork, cleaning and polishing till it looks like showroom, and that's all very well. However, what is not present on a showroom car or truck is that build-up of mud lodged behind the sills, between the sills and the floor-pan, resting above the return lip of the wheel arches and generally in the spray field behind each wheel. This mud and silt gets wet every time it rains and holds moisture well into the next days, weeks and months (depending on the climate) where water (particularly salt water in the winter) is etching its way into the stone chipped paint which is also prevalent in these same areas of the bodywork. Chassis too gets filled with debris, grit, sand and mud over time, and all these areas need to be regularly washed free of mud to allow them to dry out and stay dry for as long as possible.
Dinitrol, or any other underbody or cavity treatment will, if applied to clean painted (or unpainted) surfaces, resist to some extent moisture from coming into contact with the steel, but a maintenance regime of underbody washing, a well aimed jetwash once a week and after any off-road trip will have the most effect IMO.
I'm out every weekend doing something muddy or dusty in my truck, but every Monday when back in the city, the truck goes to the car-wash and gets a good jetwashing underneath. It took me months to "train" the guy there, he was happy to get the paint shiny and spend time leathering afterwards. When going to collect the truck, I would run my fingers around the top lip of the wheel arches and there would be a build-up of mud, still there after the wash. After bullying him and coercing him with tips, he's now making the effort to spend more time under the truck than on the surface. it's clean there now and dries out in no time when the weather is not damp and humid all the time.
The 70 seems to suffer more than other models from the arches rusting, so my advice would be to have a friendly chat with your local jetwash operator or better still, to get your own. I have a 280 BAR (3,900 psi) petrol driven jetwash which works well although I would say it's the minimum pressure that you should get, a higher powered one would be even better. I think the commercial units are more like 450 BAR (6,300psi). A little care is needed with high pressure where it can actually strip paint and other protective measures if you're not careful.
Anyway, the long and short of it is to remove the mud trapped in corners, fillets, angles and other paces water goes, leaving deposits behind to rot away your pride and joy. I like to pump a little clean oil into the air vent holes in the chassis members, this creeps around and up the sides of the boxes over time, which helps to repel water sitting in the corners of the boxes and channels. Check that drain holes are free to allow water to escape these areas and to ventilate the boxes and hidden closed areas of bodywork.
) so all that's been collecting under the truck has been some dust, but now it's raining, it's time to get the jet washer out again!
