It has been a long time, but the last time we stayed Blackwoods campground it was VERY tight for anything over 30 ft. There were some big TT and motorhomes in there, but they were getting all scratched up driving around the campground.
The private campgrounds in the area are usually booked up well in advance of the season. Many times the very beginning and end of the season really opens up (and can be chilly!).
Assuming you haven't been to Acadia, it is gorgeous! If you have them, bring bicycles - the carriage roads are fantastic to ride on. At least one morning, get up really early to see the sunrise on Cadillac Mountain - it is the first point of land on the continental USA to see the sun... just cool to see.
Acadia is open at night! We found that Thunder Hole is especially neat at night - no one else around, booming waves, beautiful stars.