Nico -
Not sure where you live, but years ago I had my S4 Elan painted by Bob Groat at Aesthetic Engineering in Sebastopol, CA. I think he's still around and doing business. I just did a check on the web, and there was a listing for Aesthetic Engineering in Half Moon Bay, CA now (650-712-8100) - not too far from Sebastopol, but not sure if it's the same place. You might check with some of the guys in the Golden Gate Lotus Club on how to contact him.
Anyway he did a great job on my car. He did the whole thing, stripped it down, rebuilt some areas of fiberglass, completely redid everything - so I can't comment on doing any of the prep work myself, because I didn't.
You can see pictures of the results in the Series 4/Pictures section here. The top picture is fresh from Bob's shop. The other two are about 12 years latter, so you can see that it's held up well.
Erv Schweiger
Chicago, IL, USA
1970 Elan S4 DHC