AFAIK- In Montana a "Concealed" weapon is defined as one which is wholly or partially covered by wearing apparel.
For more official, and certainly more accurate information, check out packing.org or the MT Attorney Gen's website.
I don't really keep up on this sort of stuff because, well, I have a CCW so what's the point in me worrying?
Yep, I-M-A-WMD has it correct. Actually, backpacks, fanny packs, purses and such are NOT considered wearing apparel, so you can carry in those types of places without it being considered concealed. Also, it's only required to have a CCW permit within city limits, to carry concealed. That means, you only really need a CCW permit it less than .5% of the state. Of course, within city limits is probably where you probably need to be carrying the most!
There are NO laws pertaining to firearms in vehicles at all, other than some pertaining to hunting from vehicles. Most cops here assume people have firearms in their vehicles, and tend to be more suspicious if you claim you don't have any.
I have a copy of the Montana gun laws, so if you have any more questions I'll try to answer them.