I masked them up carefully so I could brush paint them, as it's virtually impossible to spray inside the gutters properly. I've seen countless Pops painted beautifully, but with no paint on the backs of the gutters. As they rust badly as std this seems the best way around it.
   
You can see my little masking tape 'gutters' to catch the excess paint as it runs out of the gutter rails, 4 coats in total.
 
This is out of sequence, but I just found this photo of the finished doors showing the insides.
   
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