That musty RV smell drove my wife crazy and she insisted the OE carpet be cleaned and ultimately removed. I had steam cleaned it and the furniture 6 times since we bought it a few months before. It was in excellent shape. But I tore the carpet all out and replaced it with vinyl peel and stick tiles. Most (80%) of the musty smell disappeared with the carpet and hasn't returned. (BTW, The carpet backing and pad were spotless.) I'm sure more of the mustiness would leave if we recovered the furniture with a leather-like product.
Just another instance when she was right and I'd rather not admit it.
Carpet & furniture stored in a high-humidity environment has to be expected to become musty. The foam padding absorbs the moisture.