Race with the Devil/Fridge

Fridge Logic:

 * The cultists are shown to gain access to the RV several times, killing Kelly's dog, hiding live rattlesnakes in the cupboards, and slashing the tires on the dirt bikes it's carrying. Why didn't they just slash the RV's tires, or destroy its engine, or puncture the gas tank? Unless the cultists' goal was to fuck with the heroes before killing them, this would've saved them a lot of trouble.