Rockcrawler,
We also have a 2001 Tradewinds LTC. National had a dust problem with them from the git-go. In fact, most of them will have black streaks across the ceiling/headliner where the braces are. We've only had ours three years, but I understand from people that purchased them new, there was a recall and they installed a wooden frame. On mine, when you open the engine door, you can see a wooden structure on both sides and across the top, I believe it's just above the taillights. This was supposed to eliminate the dust problem. But my DW says there is still lots of dust.
On your gravel road, I can see where it would be extremely dusty with your side radiator. In my case, times I have traveled on a gravel road it seems like there is a dust storm swirling around me. But only when the side radiator fan is on. It's controlled electronically and you might consider a cut-off switch so you can turn it off for that one mile.
I never thought about our MH being that dusty, but I don't dust either.

We've had our Tradewinds for over three years, and I do all of my own service work and am familiar with a few things about it.
One important thing I found out is servicing your air dryer, which takes moisture out of the air lines and can cause alot of problems. If you're not familiar, it's a large cannister located just above the slobber tube which is just behind the left rear axle.
I hope this helps. Feel free to call me any time about any problem you might have, or just to chat.
Happy New Year,
Larry