We got a dog potty for our Patagonian Cavy, hoping he'd use it. It had a fake grass swatch to put on top. The animals all LOVED it... but shredded it. They did not ingest any of it, but completely destroyed it in less than a month.
I'd stick with something soft and washable like polar fleece or towels for the cage. To put over the bottom, of course. Coroplast and linolium, as mentioned, are great and safe surfaces to use. The blankets will be soft to lay on, easy to clean, and also many rabbits enjoy rearranging and digging in blankets.