A friend of mine used to do valeting and found the same problem, this time of year it was hard to polish anything because it wouldnt go off enough to be worked, getting upholstery dry was a nightmare as well.
In the end he took on the work of a smallish forecourt through the winter as the owner had a lockup he could use to do his stock in, and when there wasn't any stock to be cleaned he could use it for customers cars (think he used to give him a fiver a car that he used it for), during the summer he would employ someone to do the garage work while he was doing mobile, Andy