There are few hotels with chargers for guests, your best bet would be to charge to max at the Brownsville SC’s, there are 2 locations. I’ve done this trip 3 times and camped at Raptor Roost and plenty energy left to get back to Brownsville or Harlingen. There’s campground named Rocket Ranch that has a 1 Tesla charger but almost always busy.Is there a location close by to charge ?