Years ago, I lived in Southern New Hampshire among folks who started Gap Mountain Mountain Permaculture which is no longer operating. Two of the folks who lived there, Doug Clayton and David Jacke, designed and built what they named the Mouldering Toilet, which they built as an addition to Doug's house, not a separate building. If you look up Gap Mountain Permaculture, Mouldering Toilet, you will be able to find many references to it and praise for the design. David Jacke went on to co-author Edible Forest Gardens with Eric Toensmeier (
https://www.edibleforestgardens.com/about-the-authors) which many of you probably have on your bookshelf. They have written other books as well.
This link has a drawing of the plan in the below link. I saw in another post when I googled Gap Mountain Permaculture, Mouldering Toilet and someone was asking about it David replied and said he would pm her. With further exploration, you might be able to find out more.
https://prospectrockpermaculture.wordpress.com/2014/05/23/herbal-labyrinth-sacred-geometry-and-holy-defecation/
Although it's been many years, I remember that it didn't smell, the pee didn't make everything soggy due to the design, they used sawdust or shavings for carbon and it was two chambered in addition to the small room being a pleasant light filled room - windows) Doug and his wife would use only one chamber until it was full, then let it sit for a few years at which point they would dig out the perfectly decomposed humanure to spread on their fruit trees. It was also built on a slight slope, but I can't remember how much of one. Doug had worked for someone (probably in the 70s) who had a Clivus Multrum, a commercial composting toilet from the 70s and into today and that was very stinky because that early design didn't deal with the pee properly. A very unpleasant job and a learning experience that helped him and David create a much improved model
The Mouldering Toilet design worked very well and is worth exploring. Like others here, I have no idea how it wouldn't be cold in the winter but good luck!
Dave Jacke, if you see this, I hope I remembered this right and that maybe you can e of more help. I haven't seen you since those times but permaculture has been very important in my life and may thanks to you and Doug for introducing me to it.