If you want to boondock right on/over the water, the Sunshine Skyway fishing pier (South pier)is a great place. I have camped there two different times. No hookups, no nothing. Bathrooms and security on the pier though.
Here is a link to my trip there...
Here is a link to their website....
Sunshine Skyway Fishing Piers - The World's Longest Fishing Piers
From the bridge to the FSR, it is about a half hour. Call ahead and check to see if your rig isn't too big, as they recently redid some of the piers and you have to make a U-Turn at the end rather than being able to drive around. The South pier is nicer and the views of the bridge and water are spectacular. Bring a fishing rod.
Here is the link to the Skyway bridge disaster when a ship knocked out the bridge and cars plunged in to the drink. Very scary.
Sunshine Skyway Disaster