Parking at 3 euros per day away from Reus? Obviously in a secure compound? Who holds the keys? An easy way to rent out your car while you are on hols,it would not be the first time, it's already happened at Gatwick as well as parking your car in roads just out of town where its not too populated but vulnerable to vandalism or theft. I take it that this guy has in place the insurance to cover anything(or is he moonlighting?) that may happen whilst you have put the car in his care.
Advice?................Let the train take the strain! Train to Barcelona Sants, take the connection to the Airport, cost? 22 euros return at the most from Tortosa, must work out cheaper than paying the parking, and fly Easyjet, just got a flight for 24 euros single back to UK........AND, no parking fees or worry, is the car going to be there when I return?
      I rest my case,............hand baggage of course!