Try the local sign shops...in Europe and the UK it's called Corex and Coroflute. In the US it's biggest use is for cigarette and cola signs at gas stations. Check this out
http://members.cox.net/deantuinstra/Signs/Signs.html

Hot glue does work...unles the temps at your field get to 90 degrees F or higher...then it tends to let go. We mostly use CA glues (there is some preperation required)...there is a ton of info on the hints and tips pages at http://www.spadtothebone.com site, there is also a forum here at RCU devoted to S.P.A.D.'s as well as links on the Spad home page to several more spad forums. Also, if you go to the Spad originals link from the home page, you will see all the plans listed...and they are mostly photo essays on how to build the planes...with lots of close-up shots of the Coroplast (Correx).