Hi chrispain
The route you posted may work with newer vehicles 2004 ish onward's as they have a "Certificate of Conformation" this "COC" did not exist in the early 1990's.....
So you have to try to find a Technic who will take on a motorhome, don't forget before it can pass the ITV it also has to have Gas & Elect certificate's.
I will be trying the Assessoria Milian   on Monday and as he is down towards the Spanish Catalan border that may be what "JamJarChris" meant ?
Fingers crossed