Tony,
Doesn't surprise me that you would tackle this particular subject! 
As to your question about the paint work, the standard process was for vehicles to be finished at the factory and then shipped to depots in Italy before going over to N. Africa. It was at those depots that the "Tropen" scheme was applied. While we like to think that the Germans were always super-efficient in everything they did, that wasn't always the case particularly in the early stages of various campaigns. 
Interestingly enough, many "Tropen" features that were added to allow vehicles to operate in hot climates became standard features as it was just easier to build them all that way as opposed to trying to designate some as "Tropen" and some as not on the production assembly lines! 