I have found that starting very early in the day helps. We have done a fair few 4 hour trips and the ones with a 6am start are much better. I would just wake bubs with a nappy change, then she would have a good feed and would go down for 3+ hours. Later starts we would have a cranky bubs. Not sure if that helps or not, but atleast with an early start you should hopefully be not so rushed.