considered a "locked container"?

yes...

I use a gym type bag with a small master lock through the zippers and the ammo in a seperate unlocked pouch.

AFAIK, there isn't a specified definition.

 

What if I zip tie those two zippers together?

Any securely tied package will work. You could tape a box shut with a gun in it, zip tie zippers, use dental floss on the zippers, etc. As long as it takes some effort to open the package you'll be ok.

Yeah, the law does say tied, in some posts "locked" as well, but AFAIK, there is no definition of locked. I use the same thing with my cheapo soft rifle case, it has a cloth loop.

I carry all my handguns in a paper grocery bag...

Yep. That's how is lock all my bags. I bought 2 4 packs of travel locks on amazon and each set uses the same key.. so 8 locks.. 2 little keys. Works great for me. And since the law makes no specific distinction on how to secure the "container", I'm more than comfortable with this method.

The lock isn't about security... its about abiding by the law. Your house locking habits, a gun safe, and use of a trunk is what will keep your guns in your possession.