most alunimum parts like that have a powdercoat finish. the parts are charged and they go through a paint booth where the pigment is in the form of charged solid particles, blown around and find themselves attracted to the piece. then it goes through an oven , that bakes the paint onto the component. since the paint has no solvents it is better for the environment.
in the past aluminum parts were painted. Paint doesn't' stick to aluminum well but the powdercoat paint sure does. I'd try to stick with the original finish if you can, if not it can be painted over and then you'd be using a metal paint.
powdercoating requires the thing to be really clean so things can be etched or sandblasted to recoat but this isn't something you'd do at home. when the parts are new and still clean it works well in the factory. I've never seen that peel.
on drawback in frames of aluminum is that unlike wood or plastic is a great conductor of heat which isn't a great property for a window frame that you wan to act as insulation but as a storm it's probably not a huge issue. it's more of an issue if the window frame is aluminum and exposed to both, the cold outside and humidity and warmth inside. once you have a second window that is of less concern as there is a thermal break in the design.
some of the plastic windows have captive air cells in the design and the air is an insulator. You won't see the plastic ones getting wet from humidity in cold weather but you may see that in some cases with aluminum frames. the plastic degrades eventually from UV but may last quite some time. the aluminum won't degrade from sunlight and time. in it's raw form plastic is cheaper than aluminum.
when I grew up we had single pane alunimum double windows , they worked fine and they had an air gap between them. when it got really cold you could only see frost which gave a closed in feeling. If we opened the inner windows for a time it would clear up the frost so we could see out again. we had enough room between the two windows the cat could go in there
we had a picture window with an aluminum frame. It would form large icicles inside the house in cold weather because the aluminum's heat conductivity brought the cold in and it met the warm moist air inside the house and formed ice. that window did have a "thermopane" ( closed cell) window and that didn't frost up so we could see out, but ice formed on the frame. I remember it an inch or two thick near the indoor sills in very cold weather like -40 here in Vancouver we dont see weather that harsh.
same with a storm door, because you do have a door it isnt' really exposed to the inside humidity and the air between the doors will act as separation . You wont see that effect there as you'd close the door in temps that low.
