I have been kicking around buying one of these cabooses.
If you are worried about dust, you might use a skylight filter similar to what is used on film SLR cameras, only on a smaller scale. Some older video cameras that used a cassette the size of a cigarette pack had a lens roughly 20mm in diameter. That might be too large, I might have a few lying around. Might have to look at a caboose at the dealer if it’s still available.
Now a 90mm skylight filter from a large format lens.......that is a different story.