Once in a while I will use compressed air. At times if and when I end up swapping preamp tubes I will notice some aluminum dust on the circuit board around the preamp sockets (not really an issue with the V as the tubes hang below the amp chassis unless I am doing a tube roll with the amp chassis inverted). Not just the Mark V but the Roadster or RA100 will get some cleaning with compressed air to remove the aluminum dust caused by the tube shields, so everything gets a shot of air including the cabinet (try not to hit the speaker cone on a combo amp).
Outer ledge on outside of cabinet in front of speaker grill and the grill itself I will use vacuum with a soft brush head to clean dust that may have accumulated if the amp was not covered when not in use for some time).
