No, I just got a simple drawstring pants pattern from Walmart. I'll make the inner layer so it fits, straight off the pattern. I'll use the pattern for the top part of the outer layer, making it two sizes bigger than the inside. That should allow for ~ 1" of insulation in between. The pattern doesn't allow as much size difference in the legs, though, so I'll make the outer layer straight-legged. And allow some extra height on the outer layer too, for darts. I'm pretty sure it'll work, but it'll probably take most of tonight to make.
Oh yeah - I'll be testing another thing we talked about on our trip, Tim - I got 'high loft' quilt batting from Walmart for the insulation. It SAYS it's got 1/2" loft, but it lies. It's more like 3/8". I think I'll use three layers, which will make sizing easier too.
The stuff is definitely warm. I'm not sure how it'll hold up to repeated compression, and I'm not sure about its weight. Guess I'll find out! If the design works but the insulation wears out or won't loft after a bit, I can always make another pair out of Climashield or Primaloft.
I got zippers from Walmart too. The only ones they had with double pulls were for a jacket, and they're a bit heavier than I'd like. If I make another pair I'll get zips from Thru-Hiker.