4everfrio

I would go ahead and reserve the sites that available at Rio Frio. You can watch the reserveamerica site closer to your time of departure to see if any available sites come up. You have to check it every day and sometimes check a couple of times a day. If you find the dates you need, try to call the Parks and Wildlife reservation site first. Then, if you don't want to wait, reserve it online. Remember it is not in concrete until it is confirmed. I have done this and it is funny to see the sites come available. I guess some book a couple of weeks and then figure out when they can go and cancel the rest.
I have also booked single days as they come available and then go to TP&W and combine all the reservations into one. Sites will come available. You have to be "on the ball" and not wait.
We normally book 11 months in advance. It sounds silly but we get the time we want. Good Luck!!
~~~~4everfrio~~~~