I'd like to take my 18 year old twins backpacking in Vietnam. They are dead keen. I only have a couple of weeks (maybe three) and thought about flying in and out of Hanoi, traveling half way down the country and back, rather than rushing the Hanoi to HCM city route. But I am open to being told that I can easily cover the length of the country in that time. I also want to be relatively comfortable, so no backpacker dorms. Any tips, ideas?