Personally, i use soft paper towels and anytime they pee or poop, I change them completely.....
I am extremely anal about "stink"....and i swear, I can smell it before it hits the towel...lol...
my advise, switch to something easier to clean.....spot cleaning it not the answer.....it takes two seconds to pull out a stinky paper towel and replace it with a new one........remember to clean the tub/tank fully at least weekly (don't even ask how often I clean them...lol...i use A LOT of paper towels)
good luck