I've driven 4x4 vans since 1976 on Nevada's dusty, silty dirt roads. The ONLY way I've found to keep dust out of the interior is to pressurize the interior - shut all the windows and turn the heater/ac fan on high.
I've even met some hardcore off-roaders who mounted sets of double fans in the forward part of the vehicle roof to do just that - draw clean air from the front of the vehicle and ram it down into the vehicle. Positive pressure keeps the dust on the outside.
This is my 1976 Terravan. Note the vent on the roof that opens to the front...it scooped clean air coming off the windshield and pushed it into the interior.