I have two house rabbits,they have seperate cages both with their own litter trays..I put one litter tray in the living room when they are out(most of the day)They use it 99% of the time.Saying that they will pee on newspaper I have round the litter tray if I don't see them to shoo them onto the litter tray.
They are easily trained to use litter trays,bunnies are clean animals.