By creatively ignoring my children a bit, I made it. There are problems with the armscye, and it's too loose, but, if Isquint at myself, it doesn't look too weird. I'm going to make it in army print, with a longer, wider skirt, and drop the waist down to just above natural level. Maybe add sleeves. The basic design works and requires only two extra-large t-shirts. I just need to figure out how to add a loose scoop cowl neck and a sash, and I'll have my perfect dress.
Oh, and pockets. Need pockets.
I'll take a picture of me wearing it after I tweak it.