I think even on that blue plastic, a bunny that has had sore hocks is still going to be very prone to them in the furture. Is your bunny litter trained or trained to one corner? If so, I would put fleece down everywhere except the potty spot in the cage. This has helped my sorehocks buns more than anything. Also, excess thumping can cause it in adition to being overweight, because a large breed or being a mini rex or rex. Also, check that your bunnies' nails are trimmed on a regular basis. If not, the nails will grow longs causing the bunny to sit in an unnatural posture so the weight on the feet is unequally distributed. Continue checking the rabbit's feet at least once a week or so for a while to check and make sure the feet aren't starting to get bad again.