http://www.i4at.org/lib2/hmnwaste.htm

If this is going to be a fallback position or multiple weekends, it might be worth just making an outhouse. Dig deep at a permanent placement. Sawdust/wood chips are basically cellulose and will compost the feces over time (insert a lot of chemistry here). Lye or lime will control the smell (insert a lot of chemistry here) and keep the bugs to a minimum. I prefer lye as it can be made from fire ash. Fire ash will work too, so you can empty the potbelly into the crapper for composting and to make sure the pH level of nitrogen doesn't too bad (ammonia is your problem here, the lye or ash will help to buffer this out and stop it smelling really bad).

Keep something to clear out the underside of the seat in the outhouse. They will collect spiders, and spider bites were very common from this back in the day. They also used to keep a bucket of corn cobs in there back in the day, no paper... Taking old phone books up there when you visit and leaving them is a good idea too.