Oh boy, looks like there might be a -third- cult starting, first it was the foam gun, then the Cyclo now the two covers.
Yeah, the water seems to seep in more than you are led to believe. Now, with any car cover, it's most vulnerable at the seams.
Some time ago, I read an idea about selaing the seams of the regular WS cover with tent sealer (?) I never pursued the idea since the other cover seems to compensate for whatever gets through the seams.
Also, a thicker cover underneath, in my case, the Noah, provides that extra weight and padding you need in windy conditions ( given the top cover is secured down with a bungee cord or similar) as well as ding protection if other, non Autopian owned vehicles are in the vicinity.