Actually I travel quite a bit for my work, but it is almost all in the developed world - this year I will make 2 trips to Europs and one to Asia as well as several within the US. Normally when travelling I bring the Hassy with me, sometimes a 35mm, although I am increasingly getting frustrated with the 35mms and every time I use one, I swear that I will get rid of all my 35mm gear and never do that agian. The Guatemala trip is different in that I will going along with my wife, one other adult and nine teenagers. We have told the kids that they cannot bring their normal stuff - Ipods, cell phones etc. Photography will definitely be a secondary part of the trip, and I want to keep that aspect as discrete as possible. We (the adults) will all be wearing photo vests, primarily to carry documentation, first aid kits etc, and the deal is that I can bring a camera that fits in a pocket of the vest - still I don't want to exaggerate.
I have used TLRs before, and like them for a lot of different things, but still, I think that for this trip, something which can be carried in a pocket will be a necessity, and a 6x6 folder seems right to me.