I've tried everything: aspen shavings, aspen chips (sani chips), paper towels, news paper, etc etc.

I've recently settled on butcher paper as my favorite. I got a giant roll of it from amazon and can just tear off sheets as I need them. Super easy to clean, a massive roll doesn't take up much space, and I can use it for wrapping paper, craft paper when nephews visit, and whatever else around the house.

I'm rocking it from now on with my bps!