I want to add a storm collar to the flue so that it's a little less conspicuous. Most storm collars are not very deep because they're designed to shed water from where the top of a flashing meets a pipe. My dektite gasket doesn't need any help shedding water -- I just want something to conceal the majority of the orange silicone. To that end, I've purchased a storm collar that's pretty deep, and one size too big, and trimmed it to size with my aviation snips, then sanded the corners to remove sharp edges.
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Here's the link to the one I bought.
Some assembly required. Stainless pop rivets, stainless worm drive clamps.
And here's the finished product. Hard to tell from the picture, but the bottom is beveled to match the curve of the roof.
Here's how the Airstream looks without the storm collar. The plug in the top of the flue is a plumber's test plug, which I'm using to keep the rain out when the flue is not deployed until I find something better.
With the collar.
Here it is with the flue deployed.