Jim, you don't-- and I never said that you, or anyone else did. A tarp+bivy is my method.

IMHO a bivy is an optional piece of gear in some parts of the world. Even here in Colorado I will leave my bivy at home during some of the shoulder seasons and at lower elevations and just sleep under my tarp, in my bag, on a piece of tyvek.

I generally only take the bivy if incliment weather is expected or in high bug season.

A bivy, for under 7oz, is just nice to have for my comfort and mainly to protect my down bag when it rains.

Curious, what does a gortex bag weigh?