BillMFl wrote:
Once you are north of Portland US1 tends to be fairly far from many of the coastal towns
I think you meant to say "I95 tends to be fairly far..." For example, Augusta (on I95) is an hour from Belfast (US1, coast).
As far as US1 goes, some of the larger coastal towns (like Rockland and Belfast) have a bypass so you don't have to drive on Main St and sit at stop lights, but others (like Camden), you drive right through the middle of town along with all the other bikes, convertibles, tractor trailers, and logging trucks.
Towing wise, the entire route is do-able and the road itself is in pretty good shape south of Machais. It's a two-lane road with wide shoulders for the most part; 55mph for most of the long stretches, 25/35/45mph in/near downtowns. It just depends on your tolerance for summer traffic getting through some of the busier towns.
If the focus of the trip is the coast, I would say take I95/I295 to Freeport/Brunswick and US1 north of that.