I have done serious amounts of back packing in rough country. However, for me, that often meant it was desirable to take small game for the pot (rabbits and grouse as a for instance). That requires a good set of sights and because there is a certain amount of precision needed, I have ALWAYS opted for adjustable sights and a barrel long enough for a decent sight radius. I have demonstrated to my self, many times, that I can shoot smaller groups with longer barrels.
The shortest barrel that I have been able to effectively use in the scenario I have suggested is my Model 60 Chief's Special Target (3" underlugged barrel with target sights in .38 Special). Frankly, when I got it I was surprised at how well it held and how well I could shoot it. While it certainly was not optimum for small game hunting, it worked pretty dern well. It is steel but is NOT a burden in any way, shape or, form:
It also represents a decent self defense caliber and revolver.
Generally, I find myself carrying much larger revolvers in the field (Model 624 in either 4" or 6.5" in .44 Special or a 4" 686 .357 magnum). I don't find a "duty weight" revolver to be a particular burden, even when back packing.
Now, if you need a lightweight revolver for strictly self defense, then an S&W 642 will do for short range. However, the Body Guard design might be better for your uses. That becomes a personal choice.
YMMV
Dale53