i bought some big wood chipboard panels from B&Q, as one of my large hutches is like this. The only prob with these ones is that they let the damp in from the ground. So you need to put it in a really dry spot well sheltered. I would use at least two boards underneath, topped with many layers of newspaper then whatever bedding you use.
In the last place we lived, there was no such thing as a dry spot and in the heavy rains i was changing the bedding ans newspaper daily, which is a complete pain in the pitch dark, but I couldnt bear my boys not being cosy! Even thenm, when we lifted the board up to dry they were black with mould, so putting them in a dry spot is essential.
They are in a dry spot in new garden and we never experience wet bedding now. Also, the scratch and newton hutch cover is pulled out on a slope at the back so the rain runs down it and not near their hutch.:wave:
Hope you find this useful.