Ive noticed that older beans tend to spit out the coffee quicker, resulting in under-extraction.
Even when I only buy a 250g bag, the difference is sometimes noticeable towards the end of the bag.
I would think you need to grind a little finer than normal. But hey youre going on a road trip, and is coffee really that important?
Oh yeah Im on the coffee snobs forum.. Ill let others post their more valuable opinions