Hi, Ria,
I'm no expert, but I can tell you what I've done.
My enclosure, 140 square foot, is on soil - it used to be grass, but that soon disappeared.
I got my girls mid February and the ground got muddy quite quickly , so I put the woodchip down. This has definitely helped, but it didn't really see that much action, how it survives a whole winter is another matter.
I put a large cat litter tray underneath the nesting box (mine is raised off the floor) and that has kept dry in the rain so that the girls have a place to dust bathe in even in the wet.
I decided recently that I would keep them in the enclosure during the rain as I have a lot of bare flower beds and they adore getting dirty in them (they normally free range for most of the day) and pekins are not made for mud, no matter how much they like it!
When the Autumn comes, I plan to part cover the enclosure with a tarpaulin or gazebo with it's legs cut down so that they have some dry conditions - my girls never read the Haynes Manual about not liking rain and staying indoors.
I'm not quite sure how this is going to work, but, hopefully, I've got a little time to sort that out.
Hope my ramblings may be of some use.
Have fun.
x