September and October are mid season, with a 4-day minimum rental; from November the low season begins, with a 3-day minimum and the lowest price of the year, €125 a day (dates are approximate, so check the booking calendar). Campsites empty out, mountain roads are quieter and at night the Truma heating keeps the motorhome warm however chilly it gets outside. At Segimon Rental you pick up near Granollers in the afternoon and can be in the Garrotxa or the Montseny in little more than an hour.
The colour does not arrive everywhere at once: the high Pyrenean valleys turn first, and overall the best window runs from mid-October to mid-November, depending on the year and the altitude. The most famous forests, such as Irati, Ordesa and the Fageda d'en Jordà, get busy at weekends and on bank holidays. If you can, go midweek and arrive early: parking is easier and you will have the paths almost to yourself.