Tucker still uses a human baby playpen and loves it. Often when he is in his bigger ex-pen he'll whine for his playpen. He prefers to sleep there. It's nice because it is on wheels so we can roll him around the house with us. He is just over 4 months old.
I buy heavy duty shower curtain liners and wrap the mattress with it. I put a pee pad in a doggie litter box and one end and his bed, dishes toys at the other end. He has chewed two small holes in the mesh, but I resewed them and keep them sprayed with bitter bite. He'll also often chew through the shower curtain liner which is annoying, but again I use the bitter bite here too.
Julie and Tucker