A while ago I bought a Maxpedition "Fatboy" Versipack.
I am too lazy to snap a pic, but it looks like this:
I wanted it for hot weather. I found that I didn't like the concept because it was kind of purse-like. It might have been in my head but I could have swore that I heard people snickering at me when I carried it in a store. I ended up only regularly carrying it when walking the dog. In that case, I wished I got the "Jumbo" which has a water bottle side pouch.
But I digress. Out here in the Pacific NW it has been pretty hot. But not too hot to discourage me from carrying a midsize pistol (and switching to a BUG). Over the 4th of July weekend we drove down into Oregon. Not a long drive but over 3 hours.
I don't know about you, but carrying a pistol on the hip, or in the waistband (my two most common modes of carry) for 3+ hours is NOT comfortable. And before you ask, YES I am licensed to carry in Oregon.
I have found that a shoulder holster is a good (meaning fairly comfortable) way to carry while driving. Over the years I have gotten rid of my shoulder rigs, except for 1911's and BIG revolvers. I could have carried a 1911 but for summer I am in a Glock 40 mood (23 and 27 BUG). Flame away, but I like that combo for summer.
So, what I ended up was using my Maxipedition "FatBoy"! Perfect! I could sling it across my body while in the car or lodge it in between me and the car seat. Instant access while driving and getting in/out of the car. Did I mention perfect? Now I could stop and buy beef jerky at my leisure.
Inside the the Maxipedition I had packed my CompTac CTAC holster (GREAT holster). So, before I got to my destination I just popped into the bathroom and switched to my IWB.
Carrying a midsize during hot weather takes a little more effort than just carrying my Glock 27 in an ankle holster (or a J frame) but still doable. Definitely no need to switch just to a smaller pistol :)
So, long live the "man bag" (as my wife calls it).