Hey Chris
I'm in the same boat as most of us in setting up etc so I am looking for a more semi-perm idea. I have stumbled on this site which maybe of interest, since you already have the caravan
http://www.easytrailer.com.au/gallery.html
For myself picture 43 look alright as I could build a structure I wanted around it and make it "snaplock" into position and then unlock the side walls when I want to use it as a normal trailer (not very often).
Once I start going with this project I can let you know how I go.
Anth