It turns out I was choking myself to death in here with drop-ceiling dust. The dust was getting dropped from the tiles whenever I bounced around on the road, or whenever the wind shook the van. It was a very fine dust that I couldn't see until it accumulated on surfaces for a while, but could smell and taste. Not only was the dust screwing up my lungs, and drying out my sinuses, and making me cough and have scratchy eyes and not be able to breathe, but it was drying out my saliva. I had dry mouth.
It turns out that saliva is very important for preventing tooth decay! It balances out the pH of the bacteria in the mouth. Having dry mouth was like the equivalent of eating tons of sugar and not brushing, for months. And that is very likely why my teeth suddenly started collapsing on me.
The solution was simple: a huge $9 roll of contact paper, splattered somewhat haphazardly all over the ceiling, completely covering the tiles. I got it for half-off at the hardware store because it was opened already. It took me two hours to apply it.
Now I can breathe easily, my mouth is not dry, and it's only slightly noisier in here. It's also still toasty warm in here on cold foggy days, but somewhat cooler in here on hot days because the air circulates better-- the contact paper is smooth.
Such a simple, cheap solution. If I'd done this in Feburary or March, I'd probably have saved myself $600 worth of fillings (two fillings) and lots of pain.
So far the contact paper is sticking just fine. If it falls off I can replace it-- it's cheap-- or find a plastic with a more permanent adhesive to use instead.