After reading all of these responses and weighing it with my own experiences I believe that if you can moderate the temperature and humidity, even in extremes, you will be fine leaving your weapon loaded all season. Here' s why I feel this way. In 15 black poweder seasons I have left my gun loaded for 3 or more days at least 2 times,...left it loaded for 4 days or more at least 4 times,......left it loaded for more than 7 days at least 4 times,... and have left it loaded for 7 MONTHS 1 time only. In each and every case the gun fired and printed in its normal point of impact.
I believe that the procedure of clean loading and care of the weapon is the key. During the season, wheather I' ve hunted in the rain or not, the gun is wiped down with a clean dry cloth, unprimed ( remove the cap or primer) and set in the corner of a dry out-building. NEVER EVER brought into the residence where it is heated. It is left in an environment with the same temp and humidity of the day' s hunt.
I belive it is ABRUPT changes of temp and humidity that cause the problems.....and faulty loading from the start can also be the culprit.
If one begins with a clean, dry, nipple-picked and spotless weapon..... then I think you will be fine unless you carted your gun around in a monsoon with the barrell pointing up.