Disclaimer: Never been on a FHU site in Maine, generally can walk to a water tap if needed. I understand they exist, but have never looked for one.
Visitmaine.com, run by the state covers most everything. Visitmaine.net, commercial, has a lot of stuff.
Cruise ships visit Portland and Bar Harbor, makes the tourist area of Portland busy and swamps Bar Harbor, those areas are mostly like any other Cruise Port, just a slightly Maine flavor.
We stay in the park without hookups when we go to Acadia (Bar Harbor). If you visit Acadia in July I would suggest visiting the Quiet Side west of Somes sound for more tranquility, you can do about as much there, but without the crowds. Use the free shuttle if you need to go into Bar Harbor. Use the shuttle for everything, makes one way hikes/bikes easy. SIL & BIL are tour guides there, but are touring West this year for a break.
Around Moosehead you get more of the Maine Woods experience. There is a FHU camground in Abbot south off of Rt 6 less than an hour from the lake. Dumped there years ago when leaving our camp in the 100 mile Wilderness with full tanks, it was a small park then.
If you really want to delve into the Maine Woods there is a park with some FHU sites in Mattawamkeag which is about an hour from the Baxter State Park entrance which may be hard to get into. Katahdin Woods and Waters National Monument is a little further, but easier to get into. Both are off pavement within and a ways off for KWWNM.
Down east is a whole different flavor.
Black flies should be gone and mosquitoes might have left in July
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Welcome to Vacation Land.
Enjoy,
---stan