YY,
Glad to hear it went well. I'm looking forward to the shoot later this summer.
If you build an outhouse, you'll probably want the hole very deep. Also, it will begin to stink before too long and will eventually fill up.
Another option is to burn off the waste. Instead of digging a hole, just cut a 55-gallon drum in half and put one half of it under the seat. The outhouse would look the same, you would just have a small door in the back for removal of the drum. When the weekend is over, some poor soul would then take the drum downwind, pour some gas into it, and light it on fire. You definitly want to be downwind of anyone else when you burn it, trust me. Also, if you can mount a bracket or something for a pole to attach to, that would be good. Or, you could drill two holes through the top, so you could slide a pole through them and two people could lift it up. Just make sure they have a long pole, gloves, painters overalls and strong stomachs. You'll also want to keep a fire extinguisher handy, just in case it gets out of control. I'd also suggest something to ignite it with other than a match or cig lighter. Plan ahead for this part of the operation. You don't want to be the poor soul who has to kneel down and light the drum with a Bic, because you forgot to bring some paper with you. An used target would probably work for this, roll it up nice and long.
Oh, and good luck finding someone to volunteer for this detail.
Frank