I had to trim down the 6" poly brush a little bit to clean my 6" flex liner (installed in an exterior brick chimney). After that the cleaning was a snap. Last year was my first year burning and at times I had some suspect wood, but I only got about a gallon and half of fine dust after all said and done. Question - I noticed some light rusting inside the stove - is this normal or should I be worried about moisture getting inside?