I did that same type of thing with the xpen i bought from petedge.com
I put a peepee pad at one end and his bed and play area on the other end. They were about equal size.... with the peepee area actually maybe a tiny bit smaller than the play area....
I bought a second nature doggie litter box and instead of the litter I use the peepee pads.
He was only in his xpen for 6 months until he had full run of the place. Now I still have a litter box in a corner and if he Has to use it, he will...although he is also trained to go outside and actually prefers outside. I feel more comfortable knowing if he Needs to go while I'm at work, he can.
ProSelect Suite Retreat Pet Pens | PetEdge.com
I also got a Diaper Genie for the used pads, so there is No Smell of dog, etc., in my place.
Walmart.com: Playtex - Diaper Genie Elite Advanced Diaper Disposal System: Diapering & Potty