(Middleburg, FL, USA)
I've lived in Florida for 31 of my 38 years, but never camped much -- my mother is a New York City native who thinks that camping is a hotel without room service (LOL). We visited just about every beach in the state, but never camped or snorkeled.
My first introduction to snorkeling was at the glorious, gorgeous Ginnie Springs. We drove up to a "primitive" camping space (no electricity, and as far away from other camps as we could get!) right on the Santa Fe River. After making camp, we went tubing and swimming.
The next morning at 6 a.m., I had my first snorkel lesson. The water felt warm compared to the early morning air. Learning how was easy, and I was amazed at the fish and the caverns I could see just by diving under water. I can't Scuba since I'm asthmatic, but I was able to see far more than I thought I'd be able to just by holding my breath and going under water!
I do suggest snorkeling early in the day, before the sandy bottom of the springs has been stirred up by activity of swimmers, suba divers, and snorkelers. It gets a bit hazy when everyone is in the water.
I recommend Ginnie Springs for snorkeling as well as for their other activities (canoing/kayaking, tubing down the river, swimming, etc.). Their campsites are well-kept and you can choose to go in your RV or to camp in "primitive" mode with tents.
It's a gorgeous place, and beautifully kept. Go!