What kind of seal should I use for my storm window; and where can I get it?
Search strings: vent window seal, storm window seal, sealing tape
Technical Editor:
I believe that the tape P/N that LP Aero sells for this purpose is SP-FT132. It is a quarter-inch wide by 1/32″ self-adhesive sealing tape. Very thin and conformable.
Make sure that whatever you use is very conformable. It should have almost no resistance to being squeezed flat with your fingers. If you use anything that makes the window the least bit difficult to latch, you will probably develop a crack in the main window over time. This most commonly occurs on the lower aft radius of the cutout in the main window.
These diagonal cracks can also be greatly reduced by adding a sixth screw aft of the hinge line screws, with the same spacing. Adding the sixth screw helps ensure that the main side window has the same stresses on both sides of the storm window cutout, at the lower aft radius.
The seal also needs to be a closed-cell foam, or it will wick water. Install it with the butt-joint on the bottom aft corner. It gets applied to the storm window, not the main window.