Understand that waterfront on Key West means that you are not lounging next to your camper but in front of it. Yea, it's crowded but still worth it.
As for Periwinkle, a neat place but about 2 blocks from the water. Still worth it concidering the water tho, the beaches are quiet.
I prefer Red Coconut in Fort Myers Beach, The spots are tight but a little more than Key West. The advantage there is you are directly ON THE BEACH. A guy places boards out beyond the parking pad and gets you out on the sand under the Palm trees. I just keep my awning down enough that the guy next to me only sees the top of the awning, but it doesn't matter because you will spend all your time in front of the motorhome under the trees looking at the shoreline. A mile walk up the beach to town. Yea, it ain't cheap for beach tho, 100 bucks plus. For this you better book over a year in advance.
Knights Key in Marathon is nice, one of the best beaches in the keys. Lots of nightlife and the snorkelling is as good as it gets. I will be there in May, but even off season you are talking close to 100.
Port Canaveral has a place just off the beach that's ok and cheaper. They have been fixing it up a lot lately. Lots of nightlife, a great beach with only a short walk.