LOL Give Up. Our couch doesn't have a skirt either and you can barely get a hand under it so it is a pain in the but to clean. So I know how you feel. I have to move my couch to clean under it.
This is what I thought about doing recently on one of my sleepless nights of thinking. Turn the couch over and meauser it for a board. I am thinking two inches would do for my couch and however long you need it. The velcrow it on to the legs of the couch. As far as towels....My child would just push them under farther than I could reach or pull them out to build something!