G'day and welcome to the forum. Great choice of vehicle
Mate, all canopies will let some dust in around the bottom corners of the rear window. My ARB seems to stop most dust ingress but a little extra foam seal has stopped 99% of it.
With my ARB canopy you can option a forward facing vent which forces air into the canopy to pressurise it and slow the ingress of dust. Seems to work fairly well but works a lot better if you seal the tub first
The problem is the tub. Trust me, after my Central Oz trip last year, I learnt all about dust and where it gets into the tub.
The tailgate is not sealed at all, afterall it has to allow water to drain as it is normally open to the elements, so sealing the tailgate is the first issue to address. There are some tailgate seals on the market but a trip to Clark Rubber should set you on the right path.
Next is the floor of the tub at the front near the cab. There is also a gap here to allow rainwater to drain so a squirt of clear silicon is needed to stop the dust coming up through this gap.
There are four holes in the side of the tub. About 5-6 mm. Either a rubber gromment or a bit of gaffer tape will seal these.
Lastly there are four large gaps/holes under the top rail of the tub. These holes are between the inner and outer skins of the tub. Great for running cables etc but they allow a heap of dust inside. One hole each side of each wheel arch. I initially used a bit of foam to fill this holes until I had decided where to run my electrical cabling. I didn't end up using these gaps/holes so used some spray in space filler foam to seal them permanently.
Good luck
KB
