We use 3-main dome tents for every 2 climbers, unless you book a single tent. See our Kilimanjaro page for images of these tents. This will mean that there is room for 2 mattresses and sleeping bags, and some room for other items, but your main duffel will fit in the alcove under the fly sheet of your dome tent (outside). If you have a single tent, the tent will be a little colder, as only your own body heat can warm the air space inside your tent.