Love Acadia and Maine we go up every year
Oceanside KOA was on our bucket list. Stayed on a Oceanfront site($$$$ and yes its on Frenchmans Bay which is still part of the ocean) ,all the ocean front sites are WE only. Narrows 1 and 2 have large sites. We generally stay at Bar Harbor CG which as has been said is first come first serve and cash only. It has good size FHU sites and some nice tree covered WE sites by the way there is a short walk thru the CG to a BBQ/ice cream shop next door. Just down the road is Jack Russels steak house
Hadley Point and Smugglers Den are also nice CGs. We ususlly stay 2-3 days at Schoodic Woods since it opened. Beautiful CG with pullthru or parrallel sites WE only and be sure to get to the dump station early if its departure day. Schoodic point is a great one way drive that is terrific to bike
In Winter harbor there is a Ferry To Bar Harbor( nice way to miss the trafffic) and of course there are free buses on Acadia and Schoodic