I remembered that Ken Z. is a member of the Elks, and quite often has traveled using the Elks lodges for a nights stay. It does turn out that San Antonio has a lodge with parking for 2-3 coaches (according to their website).
Not a help if you're not a member, but something to think about.
What about colleges? Anyone ever tried parking in a university lot? The other thing I have considered is trying to find a large business park area with a large lot.
ray