Hi all, thank you so much for your helpful tips and suggestions.
To give you an update, we contacted Vilanova campsite and this was their response:
“Sorry, we do not store caravans. There is a caravan storage about 800mts distance from the campsite they do a minimum rate of 1 month ( about 85€ depending on the size of the caravan ). We do not have a website for them but we call them Gargallo”.
We got a response from Nauti Caravan who said they can store at a cost of 15euros a day. To book this they sent a link to http://www.parkandflybcn.com
which I believe is a sister company. It all looks legit so we booked online and were advised on the email comms to give dimensions of motorhome when booking. You pay when you park and there are no height restrictions. 24hr staff, surveillance cams and free airport drop off. Will let you know how it goes!
The other suggestions for caravan storage look great also but we’d already booked. Will let you know how it goes!