I just recently got a Frio pack to put a vial of insulin in when I am out doing field work (also 100+ degree). So far I have been pretty happy with it, it keeps it cooler than the outside temperature- not like keeping it in a fridge. It basically takes the edge of the heat. It works by evaporative cooling, so if it is in an airtight container it won't work. You want to try and keep it in an area that will have a bit of airflow, but out of the direct sun. So don't bury it in your pack but do not have it in the top pocket or someplace the sun is going to be hitting the most.
I have thought about buying a plastic case for it and then drilling holes in it to get airflow- but I haven't tried that yet. I haven't had any issues with it getting the rest of my stuff wet, after I soak it I try and let it drip dry a bit, or use a towel to soak up the excess water. It does help a little to protect the vials with the cushioning to keep them from breaking, I have heard of some people use old film canisters to put their insulin in then put it in the Frio pack. I don't think mine would fit, Apidra vials are oddly shaped.
The Frio is also supposed to help keep things from freezing- but I have no experience with that.
In the past I have just buried my insulin in my pack with an ice pack (that usually isn't cool by the end of the trip) and hoped for the best.
Your trip sounds awesome! How long are you going to be out for?