Here's what we recommend:

•   Purchase the storm door locally. You will have a much better selection, it will cost far less, you won't have to put it together (they usually ship "knock down") and you'll be able to arrange for installation together with installation of the pet door at the same time. Problems are much easier to resolve locally as well.
   
•   Remember that the pet door you buy must be "self-framing" and it must accommodate doors as thin as the storm door--which you should measure.  All "self-framing" dog doors have an adjustment range and for some, the adjustment range doesn't cover a thinner storm door type door.  These adjustment ranges are given for all self-framing pet doors on our "Pet Doors for Doors" page.
   
•   Use a high performance dog door.  If you need a storm door, you probably need one of the better performing pet doors as well. We recommend sticking with one of the "4 Season and Severe Climate Use" models we've listed.
   
•   Mount at the correct height for your pet. The height that the pet door is installed at, especially in the larger sizes, is critical to the comfortable use by your dog. You'll find it easier to get this right if you are supervising the installation yourself.