boat camping ideas

I would like to take my wife boat camping for a weekend this fall and am looking for some ideas. She is an outdoors girl and we like to get out and find some romantic adventures in remote and scenic places. We have never boat camped before so this will be something new. I am looking for someplace within a 3-4 hour drive of the Temple /Belton area where I can launch our 19 ft Bayliner and drive the boat a while to camp someplace remote along the water where we are not in a state park but not tresspasssing either. Being a kayaker, I am thinking about taking the boat upriver from the main lake and camping on a gravel bar. Obviously the river channel has to be deep enough to get the Bayliner up there. I am studying maps and planning on scouting good candidates ahead of time, but would like to know if anybody here has some good ideas. Hill country ideas preferred ! In particular, is going up the Pedernales River, Llano River, or Sandy Creek possible, even a little ways from the main lake ?

90% of Texas is privately owned. The public areas are not going to be secluded. Some rivers you can camp on the gravel bars but stepping on shore would be trepassing. I've known people to camp on lake islands like on Caddo. Good luck in your research.