i've got a 28 cnt wineador and use about 6 large 69% packs and about another 8 smaller packs (get them free when buying boxes.) The space is constantly full so i think that helps with stability. also have cedar sides (the cedar you get in cigar boxes). with my experience more packs provides piece of mind.
i find it is stable at 63% humidity.
i use to use kitty litter but found it does get quite dry so replaced with boveda's about 6 months to a year ago and its much more stable.