Thanks guys. I had plenty of time to think about it
The dust test. Having run a tonneau cover for near on 10 years I have tried dust seal kits, rubber adhesive moldings, blankets and towels around the tail gate gap to stop dust from coming in. What worked the best was a off cut of 2.5" PC pipe and a 90° bend to form a cheap snorkel. That only cost a few dollars but worked well... as long as it had unobstructed air flow and the gear underneath didn't block it.
It looked a bit stupid but only used it when going Bush.
So I found a good 40km bull dust track to test out the ARB vent
The dust is ultra fine. Was talking to a bloke who did outback vehicle testing for Toyota - apparently Zthe engineers at Toyota say the Australian dust particulate size of the red dust is the smallest anywhere in the world. Has implications on air filter micron.
Anyway, this was a semi used piece of wet wipe after 40km track
yep, still had a towel over the rear gear... old habits. Without any positive air flow or dust seal this entire area would be completely covered in dust even thicker than the outside tailgate panel
The system relies on clean air coming into the vent. Passing the occasional on coming vehicle quickly allows very little dust ingress but following a convoy or road train for any decent distance will fill the canopy with dust.
Have seen air filters and fans added to canopy vents but it's more sh#t to do and more to go wrong. Will run this for a season and go from there