Amazon has some that you plug in and it dries up accumulated moisture and use it again.I think their are enough desiccant products that are not only effective, but reusable that
this shouldn't be an issue any more.
If they do accumulate dust on the carpet liner, I haven't noticed. My doors are also carpet-lined and I don't see dust puffing off the doors or the ceiling of the topper when the doors slam shut.Worst aspect of carpet lined toppers I've "heard of" is how they'll possibly/likely accumulate dust. Whether they are vacuum-able, IDK. Sealing the truck bed seems like a good approach, particularly around the tailgate.