In the ceiling of our motorhome are a series of register and return vents for the three ceiling AC units; the air is sucked in on the right side, cooled (or heated), and blown out the left side:

Here’s a closer view of one of the intake vents:

Looking on the reverse side, you can see that each of them includes a foam filter to catch dust:

These filters need to be cleaned every few months. But we decided to try some replaceable filters from RV Air, that should do a better job than just a thin bit of foam:

A comparison of the new and old filters:

An old filter, showing the collected dust:

The new filter installed:

The vent back in the ceiling:

About half of the ceiling vents are a different kind, for some reason:

These ones are attached via a clip in the middle, so need a different style of filter:

We’ll see how these new filters perform; I think they’ll be an improvement.