Frank Ettin, you more or less nailed the technique I practice.
Exception being, I take more of a step back with the strong foot (or forward with the weak foot, depending), into a hybrid of a martial arts front stance and side stance. IE, blade the body into the threat.
The weak hand could be brought to the chest, as you described, but it could also be used to strike, deflect, or fend off an assailant. (Keep line of muzzle below line of support hand and arm.)
With regard to weapon retention, the cross-draw isn't (to my mind) more problematic than strong-side. Here's my rationale:
1) With strong-side, if one is unaware of the threat, a grabber can move in from the rear or flank and grab the gun. (Edit: My usual defense against this, in practice, revolves stepping forward or back while rotating my hips and jamming down on the grabber's wrist with my strong-side hand; let CG and body mass do the work; lots of potential torque involved. I don't care how strong the guy's forearm or grip are, wrists do not typically win over hips.)
2) With cross-draw, grabbing from the rear is extremely difficult, and from the flank is difficult. An attacker to the front has a better chance of a grab, but should have a harder time surprising the carrier.
So I could see cross-draw being a problem if one were engaging in hand-to-hand, but I see it as less of a problem for a surprise grab.
Also, by blading (as previously discussed), the carrier can move the grip to an angle that can really apply some nasty torque to a would-be grabber's wrist. (See a pattern with stepping, rotating hips, and using mass to torque a joint? More advanced - bend knees slightly and drop body weight through the turn - torque from body mass and inertia, plus weight from gravity. Be very, very careful trying this with your friends, as you can tear ligaments, break fingers, etc. If you try this, do it with blue gun or red gun, and do it very slowly at first. Better yet, find an aikido or jujutsu instructor, and learn it in person.)
(Note that I used to train in iaido, the art of attacking from the draw with a katana - the sword is carried cross-draw, and the techniques one would use for defense against a sword grab work really well in practice with blue guns in cross-draw. I've tested some of these in aikido practice.)
Caveat: If we were doing this in person, I'd have you sign a release form. Please bear in mind that I am not your instructor; I recommend you find a local instructor; and I've warned you that some of these techniques could very well result in injury to training partners.