Thanks for the suggestions, folks. I knew you were a good resource.

Chris K. : I know you're right. My problem is that the outfitter for this 3 day Canadian Rocky Mt. packtrip will permit only a fanny pack on me while mounted, and a "roll" holding coat/rain gear "tied to the back of the saddle". They never mentioned a pommel bag. I guess I could buy one and try it, but the ones I've seen don't seem large enough to hold a coat and raingear. I don't ride enough to really make the purchase a good idea, but will do so if the wellbeing of the horse is at stake.

So if a jacket (insulated, but not overly weighty) and a rainsuit is too much to put in a roll and tie to the cantle, please tell me. What about draping the roll forward of the pommel??

I GUESS THE WATERPROOFING OF THE CANVAS WAS A MINOR ISSUE!