How to tempt buns into boudoir?

I have two four month male rabbits. They have a hutch outside (we live in Uganda, so it's nice and warm) and have a run on grass and a covered sleeping area, filled with hay. They are totally uninterested in the sleeping area, other than using it as a toilet (well, one of them does, the other one uses a litter box in the run). They just lie outside on the grass and don't seem to realise they can go inside, into the shelter. I have tried lining the sleeping area with newspaper and with an old towel, but nothing has tempted them to snuggle up inside. Is there any way I can persuade them to do that? Or should I just accept they are a bit stupid??!!

Food If you want to get them back in at night, get into the habbit of feeding them their dry food in the evening at bedtime, pellets in a box which are rattled as you walk over to them telling them it is food time may work after a while.

Thank you! Actually their hutch is a run is attached to a shelter, but we let them run around the garden all day anyway. What I mean is the run part of the hutch is wire so when it rains they just sit there getting wet instead of going into their nice attached shelter. I don't have any problem getting them to go back into the hutch itself since bedtime is always food time too, as you suggest. Maybe it's because the place I bought them from just kept them in wire cages with no shelter part and that's now what they prefer because they're used to it.