Condensation on windows

Hi our Bailey Unicorn is going in for its first service next weekend, we noticed last weekend while away in our van that the front three big windows look steamed up. We cleaned the outside windows but cannot get rid of this condensation on the inside it looks as if its got in between the glass somehow?  Just wondered whether anyone else has had this problem. We are having it serviced where we bought it from so will be taking it up with them.  Just hope they can fix it.  Sue