The sunseedling i have came with a fleece top to the soaker, so I didn't worry about a stay dry liner. However, you could cut up some fleece and lay it in there. I think must CD sites have fleece or even silk liners that would help wick moisture away from the skin.
Re: If you use sunseedings for night time..
I don't use SS but I use other fitteds with stay dry liners. I just cut up some fleece into strips.
I also bought one pack of bummis liners to try them out. They work just fine. Its cheaper (and easy) to make your own though if you can.