Hi Gaby08,
Re filling up with fuel.
I fill up at the BP station on the RM19. It is still a few kilometres from the Centauro depot but the car fuel guage has always still shown as "full" when I arrive at Centauro.
There is an even closer filling station to the airport/Centauro. I'm not sure of its name but its off the first (I think) roundabout when you come off the A30 and are heading to the airport. I stopped using them mainly because every time I went they seemed to have pumps out of action and I worried they might be completely out one time and I'd have to go all the way back to BP.
Hope this helps.