I think the key is taking the route along the coast as RosalieAnn mentioned, especially if you have 3 days to drive.
If you start in Reading (Pennsylvania)
instead of Philadelphia, it's possible you may want the first part of your trip to go faster since your local area is probably less interesting to explore. So you could do US-222 to US-30 then down I-83 to Baltimore
If you get all the way to Baltimore on major highways, then you could try to get to US-50 to cross over toward the coast, then follow Rosalie's directions from there.
Really though, from Reading it almost makes more sense to just go toward Philadelphia or Wilmington (Delaware)
, then just stay closer to the coast all the way down.
It just depends on how you want to time each part of your trip.