25 degree bag plus WM Flash jacket equals?

I don't have the MB, but I think your system is a good fit for the conditions you described. You will probably be a little cold on a 10 degree night, but survivabley so. Just make sure you go to bed on a full stomach and your feet are dry and you've got a decent ground pad etc. Consider bringing down booties or vapor barrier's (bread bags are fine) for your feet if the forcast is closer to 10. I think VB's are more effective for the weight though.

I imagine a lot of people would find this system inadequate but if you sleep warm I think you'll be fine.

VB! +1 Especially if you sweat a bit more than average and always VB socks!!! I never leave home without them. Bread bags work great with a sock over them. Sock hold them in place. Feels wierd for first 5 mins then its "normal". VB gloves as well. Not sure how many have used VB underwear, but sometimes its a good option.

VB half sided wind shirts are good as well. Keeps you from sweating out the back of your insulation when wearing a pack. Take wind shirt and spray it if nothing else.

How exactly do vapor barriers work? I'm not familiar with them. How do they keep your feet warm in cold temps?

Also, would a WM Megalight 30 degree bag with 2oz of overfill be a better option than the Montbell #2 for this purpose? I'm guessing the overfill would make it more of a 20 to 25 degree bag, right?

Doug- personally I think you might be pushing it a bit w/ a 25 degree bag for late fall, late fall can often be the dead of winter (take last fall as an example :))- w/ a light down jacket (along w/ insulated pants, warm hat, gloves, socks or better down booties) you can probably push a bag close to 10 degrees- that's factoring in warm sleeper (which I count myself)

a good, high r value pad is going to help things along immensely (a "summer" pad will get you cold before you even hit the rating of your 25 degree bag)

a good bivy would help you push it even a little further

a quality 25 degree bag and good insulated clothing (and appropriate pad and possibly a bivy) will certainly get you through a fair bit of Montana fall & spring, but a quality 0 degree bag (and the above mentioned items) will get you through all of fall and spring AND almost all of winter to boot

Mike

I agree that the 0 degree bag would be better…ideally I'd just have a quiver of gear from which to choose depending on the weather…but that's not likely to happen. So, I'm looking for cheaper, not necessarily ideal, alternatives.

Should have mentioned this earlier, but during cold weather months I'll be using an Akto for shelter. And at this point, probably a TT Moment during warm weather months. And right now I just use a Neoair and add a Z-Lite to it when needed.

Thanks for the responses so far. Anybody else have any thoughts?