With regards to travel from NH to ME - Do you think it's of value to boot on through on I-95 as far as we can, or would we benefit from going Rte 1 along the coast? We've done both before, but not with a camper. I'm guessing from your comments that Rte 1 is likely to be a bit of a gong show.
It does stink when you get pigeon-holed into a particular time frame but if you act quickly you might be OK. Just have multiple places in mind. Personally I'd go as fast as I can on Rt. 95, which depending on timing might not be that fast! Mid-week SHOULD be better. Do your best to avoid rush hours. Rt. 1 could be a nightmare. It's busy during regular summer weeks but that week will probably be insane. Thanks to my Yankee roots and personality I'm a "let's get there as fast as we can and spend as much time as we can at our destination". Keep in mind that campground availability may affect your travel schedule. As a back-up plan if you get stuck and can't find a cg, look at some of the hotels in the area. Some of the chains like Embassy Suites and such aren't uber expensive and often offer breakfast.