Our experience with both our first and this TT is that closing the roof vents and windows makes a pretty good seal. Last year I took ours about 5,000 miles (~8,000 km) across the US and didn't experience a dust issue including when I went through an area range fire. They're made to seal pretty well. Of course, your mileage may vary based upon age and condition of the seals but I hope that you'll be pleased.
Bill & Anne + FBs Athena, Jada & Cupcake
Wilson III: 2015 Ram 2500 6.4L Gas 4x4 4.10 CC SRW
Gypsy II: 2013 Kodiak 279RBSL with table & chairs instead of a dinette