Being a native Texan/Austinite, I'm confused at the question, so I'll give multiple answers:
1: The things Alamo in Austin were the Alamo hotel, which has long since been turned into a bank building in the mid 1990s, and the Alamo Drafthouse chain. There are some areas near Town Lake in Austin (err, Lady Bird Lake), but I don't think that is what one is looking for.
2: If you want to park in Austin and drive to SA, I'd recommend a rental car place. One could get a Car2Go SMART car and pay the ~90 bones for a day's use, but those little things ride like boneshakers on I-35.
3: If you want to drive your motorhome to SA and have a look around at Hemifair plaza, I think the above mentioned post is a very good guide.
