When we were there two years ago I had contacted the city parking authority, which gave me an address of a lot near the Alamo where RV's could park. Great! So off we go.....only to find a big sign "No RV's, buses or trucks" at the gate. So much for that idea. We looked across the street and saw an RV in a lot, so we pulled in there, only to find a sign that announced that RV parking was $60 a day! No thank you. As we pulled out of that lot, we noticed diagonally across the street two other RV's in a small lot, so we headed over there. Ah, success at last - only $15 per day. For cars the rate was $10, and since the LD takes up two spaces, I had no problem with the $15 charge. In case anyone is interested, the coordinates of the lot are 29.424845, -98.482491. This was one of those where you put your money in the slot numbered for your parking spot - we had no problems.
Have fun!
Ted H.