How and why? It's doubtless you've thought through this but at a cursory glance it seems to me like Texas would be a nightmare location for filming pre-airconditioning.The main hub for television and film in the United States is the city of El Paso in Texas.
Interesting, what of the areas that this US didn't annex that are suitable for slave holding?The expansion of slavery into warmer territories and climates predominantly occupied American colonial interests. Much easier to spend money and men into Caribbean sugar plantations than to invade, occupy, police, and build new infrastructure to support their economic system in what they saw as "untamed wilderness." There was simply no profit motive for the expansion of slavery in the plains, thus, it was mostly left alone.