wemoto do a generic k&n type filter for the rxs100.
problem fitting though . i cut my airbox in half , you need the rear part of the airbox to hold the battery. 2 mins with a hacksaw .
then you really need a 45 degree bend intake rubber to keep it out of the way of the frame . i got round this by mounting the new air filter rubber onto the standard intake rubber turning the rubber to get the filter clear of the frame . side panel goes straight back over the filter .
now looking for an expansion pipe