Cooling system capacity is adequate if it is in good condition, clean and flush thoroughly; and fit a new Daihatsu thermostat. Refill with water from a water filter, or boiled in a kettle, this helps to remove many inpurities, and use a minimum 33% anti freeze in it.

Fit breather filters to both axles, gearbox, and transfer case; i use fuel filters, lengthen breather pipes and locate in less dust prone areas as these will prevent dust entering the drivetrain oils.

Fit a pre-filter to the engine air inlet, this is basically another filter to filter out the coarse dust, and reduce the load on the main engine air filter. Fitting a snorkel may be beneficial as the air inlets may be rotated to face rearwards, and pre filters can be fitted in them.

Fit an air filter to the cabin air entry, a flat panel air filter is the most commonly uses item as these are easily moulded to an airbox manufactured to fit.

Starting at the front, grease all steering joints, remove the front wheels and adjust the wheel bearings, pack them with new grease, and replace the auto hubs fully with new grease, this will help prevent the ingress of dust. Pack any gaitors fully with appropriate specification grease also, to prevent dust ingress.
Grease all propshafts, and replace rear wheel bearing grease.

Fully service the vehicle, replacing all fluids, including all oils, filters, power steering fluid, and brake fluids.

Manufacture and fit heavy duty underbody protection from 8mm steel plate.

Replace the tyres with good off road tyres, my personal recommendation is Cooper Discoverer STT, these are ideal for desert operation due to their resistance to punctures from stoney desert conditions. These are available at competetive prices, and much less than other premium brands.

Undertake as much research as possible from expedition vehicle converters.