My current airline is trialing a dehumidifier system. This is however not for the avionics but to prevent condensation around the a/c doors and crown skin area.
It uses a rotating drum of silica gel crystals to dry the air which is then ducted to the skin area around the doors and a smaller amount to the crown skin area.
We are testing it as our airbusses (A321) have suffered from moisture pooling around the #2 and #3 door areas as a result of condensation. This has lead to carpet staining and insulation blanket deterioration and pax complaining of the cold as a result.
Not sure how effective it is but the carpet stains seem to be less!!