Well, this might sound really redneck but I used to make a "cat box" when we went camping in our no-potty Pop-up. I sometimes needed to get up at night and I'm NOT a fan of walking around in dark campgrounds in the middle of the night. So I got a regular plastic bucket, lined it with a sturdy plastic garbage bag and put a few cups of that clumping cat litter in it. Voila! Midnight cat box! We disposed of the cat litter in the usual way when we needed to.
When the kids were little we put the Cat Box inside a small tent next to the pop-up. When the door was zipped up, we knew it was occupied. When only the screen was zipped up, we knew the tent was empty.