if its dust, try using a very soft nail type size brush that you can buy at the supermarkets. Make sure it is very soft though. Be aware that any dust will blow round your 'van. Gently "stroke" the mesh - don't brush it hard. You can also use a domestic vacuum cleaner.

You can also use the same if its dirt and have the brush slightly wet - but not too wet (wet the brush and then shake the water off) so that it runs down inside your window frame - inside is a felt strip which runs the width of your window and works the mesh screen from the top downwards and the blinds upwards - don't get water onto the felt strip or you will have non-operational blinds. Otherwise try a damp cloth. Dirt is time consuming to get off.

If rusty, it will need replacing. This does not need to be done by the window manufacturer (usually Dometic). This blinds come apart easily and can be done by guys who install fly mesh on house windows (but pick a guy with some experience who wont wreck your blind as they are expensive to replace)

We use mild soapy water and an old dishcloth (dishwashing detergent)

f you do get water run into the slot below the bottom blind, its likely it will not operate again, so be VERY careful not to use a wet cloth - just damp. If its a Dometic brand (most 'vans have them) you can remove the whole window frame out very easily just by taking off the screw cover caps and then unscrewing the whole thing (don't drop it onto your feet).

Then lay it down and open it up like a sandwich and the whole mechanism is exposed. Open it very slowly as it is tensioned. You can then either replace the felt, dry it slowly (don't stick it out in the sun or it will shrink or twist) and clean the dust out inside the frame (and it collects in there big time).

I carefully watched a caravan repairer fix a faulty blind on my van - hence the info above. For our problem the blinds wouldn't open and shut easily (very common). He adjusted the tension and the felt strip and good as new