If you are asking yourself this question, you should do it already. Let me explain myself, why should I need a campervan in Seville?
Is a city where you need a transport
The underground has just one line (http://www.metro-sevilla.es/en)
The freedom that gives you the campervan is huge
From one part to another [interesting] part you need transport
Need to know what can you see in Seville?
Take a look at: http://www.lonelyplanet.com/spain/seville/things-to-do/top-things-to-do-in-seville