I travel hundreds of miles a year on gravel/flourdust roads. At first I had some trouble with it, but as I have chased down the problem areas, I have very little now.
First problem area was the weather stripping on the doors. The corners where the sealant strips met were not always together. A little flexible sealant to "glue" the ends together took care of most of that. I still have a small amount by my side door. I will eventually find where it is coming in.
Next were the floor seams. I ended up sealing these both under the trailer and on the upper part of the seams themselves.
The back doors seal pretty good, but dust settles in a pile on the top of the seals, and if you aren't careful it will come in when you open the back doors. I have a very thin nylon curtain that goes over the back door area that catches that junk and keeps it out. It is attached on the sides and top with velco tabs, and acts as a dirt catcher and a very fine bug screen. It isn't always on there, but I try to have it up before I travel.
Next was around the base of all the walls. Cargo trailers with overlapping alum siding on the outside allow a lot of fine dust through and into the wall area. I had to put a line of caulk both on the bottom and the top of the molding there. I still have a couple of vertical seams on it that I didn't do and need to.
Last was doing the back corners by the barn doors. This area is where you can access the rear lights so it needs to be accessible for repairs. Since that is also where part of my bed frame attaches and folds up against I hadn't fully sealed it off. All the dust that I thought was coming in the back doors was actually from these two vertical seams. I opened both of them up, carefully taped the vapor barrier in there and then lightly sealed the corner with metal "drip edging". No more dust in that area!
viewtopic.php?f=42&t=55219&start=120I'm not worried about ventilation. When I am in the trailer and the cargo door bars are off the doors, they don't fit very tight. I can see light and feel the draft on the side door alone. Plus I always have the top vent open and usually a window or two.
Dust from the roads can be really nasty and gives my hubby some bad allergy attacks so I try to keep it out as much as possible. We have a canopy on the truck that I gave up camping in because there is no way to keep that fine flour road dust out.