I was going to suggest brain tanning. I was watching on TV and an old trapper was saying that the brain of an animal has everything you need to tan it's hide. I'm not expert from just watching but it looked as simple as boiling the animals brain in water and then painting the hide with the liquid after you have it stretched and scraped. I've been told it's important to get any tissue scraped off of the hide. To stretch the hides they had a sheet of plywood with concentric rings painted on it to use as a guide. They used small nails to tack the hide to the plywood in a circle and stretch it.
I did help skin some muskrats once but we didn't tan them. They were just scraped, dried and stretched on a board. The people that I was helping with the muskrats did get some of their other hides tanned (deer hides and such) but unfortunately they had them done commercially so I can't tell you much.
Another friend is a taxidermist and was doing some tanning. They used a store bought tanning solution that I brought from town. I believe you just painted it on, again after stretching and scraping the hide.
