I'd like to find something to carry my concealable soft armor and a helmet in my truck. If it could fit a 10.5 AR pistol it would be a plus but not needed since I have a good case for it.

Black or CB would be ideal since it would really just live in my truck. I'd want it low profile for times a coworker may hop in, or I need to carry it somewhere.

I'd like it as compact as possible since I drive a Ranger currently.

Gym bag.

Should be plenty of options that would have the capacity for it, and it's not really something that anyone is going to question tossed in wherever or stuffed under the backseat. If you need to add some rigidity to it, then look to closed-cell sleeping pads from wallmart or rei or wherever's close. Cut 'em up, stack/duct-tape as needed, it'll give some form and stiffness to the bag as well as helping to cover over any tell-tale protrusions or bumps if someone bothered to look closely enough.

A-3 bag. You can pick them up for about $15. They are much bigger than you need for armor but it's not padded so it will just collapse on itself. It's also nice to have the extra room for jackets or goretex if needed. You can never have too many of them; I have about 12 (started making my own in various sizes).

ETA: just saw it's concealable armor. Gym bag would probably be your best option.