Storm flap for Golite Hex 3?

Only if the wind is blowing very hard will you need such an addition(very rare conditions in my experiance). And in such conditions, all you do is stake the windward side to the ground.

The golite bathtub floor is heavy and serves an unneccesary function, and should be replaced with something lighter.

I have a Hex3 and I've never experienced a problem with rain blowing under the edge. I do usually camp in forested areas that provide some buffer to the wind. If it is windy, I do pitch it lower to the ground. I do have the floor although I use it only when camping in swampy wet conditions (Tyvek otherwise).

I did sew a 16" wide piece of bug netting to the perimeter of the tent to keep the bugs out, so, I'm sure you could do the same with a "rainshield". I did it with a cheap sewing machine. The only tricky part was getting by the 6 seams in the material because of the thickness of the multiple layers there. I simply skipped over those seams.