Do you have to worry about theft from the vehicle? If so, I'd lean toward a less photo-obvious bag.
When you say "work from the back of a SUV", do you mean within a few feet of the vehicle? If so, then a flip open case (such as the Halliburton might be easiest. But not if you're carrying any distance.
In any case, you may want to use a belt pack or fanny pack for the odd bits so they're handy.
Lowepro Orion Trekker II right now; I'm looking for a new bag but who isn't?
I once used a laptop rolling case for the transport of my Kodak 2D 5x7 with accessories, it worked great.
I'm thinking of one of these shoulder bags, better for my back.
I'd like a new hard case for carry on of said 4x5 or big medium format, any new ideas.
Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand