Sorry I got here late, lightning fried my other computer 2 nights ago.
Here's my opinion of this topic,.....
Most fellas back in the early 1800's signed up to work the trapping fields in whatever capacities the brigade leaders chose for them and largely based on their individual abilities.
Some of those young fellas had apprenticed under someone for the various "trades of the day", and some had no experience at all and just wanted to experience the western adventure and a chance to make their "fortune".
As far as surviveing the wilds of the mountains, let's not forget that those that went west, didn't just get "dumped" there overnight. They had some time to learn many of the needed skills (to survive) as they traveled with more knowledgeable leaders.
I think the initial trip to the mountains for those without experience, could be compared to "basic training" in our modern military services of today. Sure,... more skills were learned as they reached the fur fields, and some of the men learned and became more proficient at those skills then some of their unforunate compadres.
Looking at this topic from a "dietary" view,... the food changed as they traveled across the plains, which gave them thier bellys time to adjust to different foods (espeacialy buffler meat), and I think most of us today, would have little trouble doing the same thing given the same experience.
I have no doubt, that for some, "hunting and shooting" was also learned (for the first time) during their trip west, and they became proficent enough with both skills to have a reasonable chance at survival by the time they reached the fur fields, and I think many of today's youths could do the same thing (within the same time period) given the same opportunities.
We must remember, that the American brigade leaders (back then) were also "mentors" to the inexperienced men in their brigades, and everyday living in the mountains could be (kind'a) compared to today's survival courses, and those that didn't learn, or those that got carelesss, didn't last long.
Are there some of us today "tough enough" to do what those fellas did back then?

,.... I have no doubt in my mind, that the answer to that question is a resounding "YES".
Although, my "days" of doing something simular are pretty much over (due to my age and health), I grew up with horses and learned how to take care of'em before I reached my "teens".
Shooting and hunting, just sort'a came "natural" for me at a young age,... and I'm sure many of today's youths can say the same thing.
I've always managed to eat "most anything",... and keep it "down" without any ill effects.
I started trapping when I was in grade school, and checked my trapline as I walked "to and from" school, everyday.
It doesn't take much time at all, to become profiecent "talking sign" (at least for me it didn't take long) and that WAS the universal language of the fur fields (whether a person was a trapper, or, a trader of the early 1800's).
Do I think I could've/would've joined an early 1800's fur trapping brigade (back when I was younger), and would I have been willing to "bet my life" that I could've survived?

.... Yeah,...I believe so,.... and I think many other young fellas (of today) would have been capable also.