Renault Boxers of the same age too. I had my bonnet repainted a few years back but it all peeled off again. Now Paul is being a total star and respraying mine after sanding it back to bare metal... bonnet and wings done last summer, doors sometime this summer. I think it's the only way.
Back on topic, I use Fenwicks motorhome cleaner on the body, often finishing off with Fenwicks bobby dazzler stuff for shine. A spray of Wet'n'forget once a year keeps the roof pretty clean and free of nasty green stuff. I can't get to the roof on my sloping drive... not now that I don't have someone to hold the ladder on the slope!

Hence the quick and easy spray at an opportunity when it's on the flat.
Not sure about the temperature problem but it makes sense that the suds will dry too fast... just do one side at a time and rinse. Oh and I had one of those wash matic brushes back in 1970 when I got my very first car!! Now I really feel old

