Hi Mackem
Are you putting straw or hay up in the sleeping area at all? That would make them likely to toilet there. Although, it being a new habitat, they’ll probably want to toilet all over initially as a way to mark it…
Did the old hutch have have a sleeping area?
Do you use a litter box in the hutch or just line the bottom with the paper and sawdust? If you provide a big box with litter material and hay in it, they should take to toileting in there. Then you could do away with the other materials altogether. Much easier when time to clean!
I rather think rabbits would not take to those sleeping areas after dark as they are too enclosed. Usually one bun will stay out in the open area on the lookout and if a pair, the other will join him/her for company.
My rabbits don’t have a hutch but they tend to sleep out in open areas. It’s only during the daytime they might go into hidey areas to nap.