Mine are hating it too, so glad it is sunny today, they came out at 6.30 this morning.
Two of them will venture out a bit in the rain, and the other sits there looking grumpy and lonely!
I realised their litter tray was getting soaked too, and felt really bad! Even the covered run seems to have been getting soaked and it was absolutely filthy with a mixture poos and water. I think I may have to block the back of it off.