Does the weather stripping need to be 1/2 thick?
No, it doesnt have to be perfect. You can use 2 pieces of 1/4 or pieces of 7/16 thick. It is because you have the mending brackets on washers to adjust for height. If the panel sits too low/high for the weather stripping, just add/subtract washers under the mending bracket to jack it up/down to make the panel as sensitive as you like.
