travelling/holidaying with toddler help please!

DD will turn 18 months next week and we are going away on holiday for 3 weeks.What im worried about is one,how will she go on the long journey,ive got quite a few things organised for that as its about 6 hours drive but im mainly worried about how she will sleep,she hasnt slept in a portacot since she was about 8 months old and from birth till that time she slept fine in it if we went away same as at home but now shes older im worried if she will be worse?Does anyone have any experiences?She will not co sleep so that wont be an option and since we are going away for so long im just really worried how she will go,is there any suggestions to make it easier for her or to make it feel more like home and her to sleep in the cot and is 18 months a horrid aid for it?should i have tried her sleeping in it more at home?arggghhh worrying!!