Going to try litter training the rabbits again

I've tried this so many times but it's not really worked and so I took the litter tray out a few months ago. Archie and Izzy are both neutered/spayed and live in a 6ft hutch with run underneath. They seem to pee in 2 corners of their hutch in the closed in part. My Mum doesn't think putting a litter tray in the closed in part is a good idea because it takes up space and if its cold it will leave less space for the rabbits in there. Although they can fit in the closed in part if they have a litter tray it doesn't leave them very much room is it ok to put a litter tray in there? Also as they pee in both corners, there's only space for one litter tray (they aren't small rabbits so have a cat litter tray) If I put it in one of the corners do you think they'd use it or not. If they don't use it, how can I get them to use it? Also what should I use as litter?

I found that the only way was trial and error, some they like some they don't. i think it just depends on the bun. I have 5/6 trays that they either wouldn't use or we just found didn't work for us