If it's tourists in rental cars... don't waste your time....that's not a market...
...consider your own situation: have you ever paid to wash a rental car while on vacation?
If it's snow birds ... people that live in the area part time, or long term lease holders (>1 month)... that may a capturable segment if they bring their own car.
...and consider the impact on your regular customer... lots of folks may get perturbed at text
marketing when they already use your wash.