I plan to visit Barcelona next month in my camper, but want to sleep (Airbnb) in the city for a couple of nights. Has anybody suggestions where I can cheaply park my camper within easy train (or bus/tram/metro) reach of the city, but with minimum chance of theft/break-in? It is a small bus-camper (Mercedes Marco Polo), thus probably attractive to thieves, and is fitted with an alarm system. Size is 4.75 metres long, 2 metres high (fits in a normal parking spot).
I don't want to have to pay for an official camp-site (most are full anyway). The ideal would be a free car-park opposite police and railway stations (;-).