Most of the turtles can be found on the west side of the park, in the narrow channel and the east end of smugglers cove. I have entered at the boat launch and exited at the docks just before the river or with lots of air continue to drift into the river. (exits are limited so you would need to plan it in advance.
I think the bottle site you are referring to is located at the east side. If you enter at the swimming beach/ scuba diver zone, then fin east along the shore line and around the point to travel north. you should find it.
There is also a small boat in about 70ft of water. it is located down from the old boat launch which is now located by campsite 105 or 106. Please note that you are not permitted to pass through the campsites to get access. But if you are staying on the one of the two sites it is not an issue.We often have one member of our group book 106 as it is a little nicer than 105 to stay on.
I am diving there on May 16,17,18. If you are in the area I can help you find your way.