NMDriver wrote:
1600 miles to San Antonio. 3-5 days depending on driving style. 60F days and 40 nights, (18C and 5C) on average. Colder weather can strike but is unlikely.
You will likely hit above freezing weather around the OK/TX border region (1100 miles). Typical nights will be right around freezing but it warms up during the day.
This is really your only option with a limited timeframe. It's a straight shot from Winnipeg and it'll be your first decent weather but golly, that's a really long drive with a RV through the northern states with a deadline. Good luck!