First of all, you should be bidding on Economy class vehicles through PL and getting your upgrades at the counter. It is a certainty that there will be SUVs available at your destination unless you have arrived to blizzard conditions. Smile and dicker with the counterperson for the SUV of your choice. She has vast bargaining authority for this.

If you can't get the Yukon or Expedition of your dreams for $10 extra and you are stuck with a PT cruiser (this never happens), head for the trailhead anyway. It is a rent-a-car, after all. True Flyertalkers drive rental Crown Vics offroad in Maui.