I am booked on the Hanoi to Singapore trip Nov.8-Dec.20 and was wondering if bringing a sleeping bag was absolutely necessary? I am planning on bringing a fleece sleep sheet anyway, and I checked the average temps. for SE Asia and saw that most regions don't dip below the mid sixties at night. Sleeping bags take up a lot of room, so do you think I could get away with a fleece sleep sheet to save space? I can always sleep in a sweatshirt...Haha.