Hi, I have a question about wool soakers and fleece covers, can they be used under clothes?

I've been using both at night just on their own over the night nappies and they've been great. But DS is about to outgrow his small PUL covers and I wanted to replace them with fleece and/or wool but I'm worried that if they work by evaporation they won't work properly under clothes and end up wetting the clothes.