Here in dry Utah, pumpkins will last until frost just sitting out in the yard as a decoration. If taken indoors so they don't freeze, and kept dry, they will last until Christmas. Things may be different if you have high humidity. Of course, that is for pumpkins that mature later in the year. I don't know how well they will do if you still have hot weather. If you can put them in a shed so they are in the shade, and put them on something so they are off the ground, they may do well.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-