a soft electric guitar bag is the perfect disguise. being a former musician I have a few hanging around still. nobody would ever be the wiser. they can be bought cheap online and usually offer somewhat substantial protection
Another option would be some of the Gator cases made to hold keyboards.
Bulldog makes a nice case that will hold just about any AR when the receiver is split. There is even a padded divider to keep the two halves protected. The case will also hold a Tavor as long as the optic isn't too high on the rail. (An Aimpoint just fits)
The stickers are essential. People suggest I put a hilldog sticker on there to complete the effect, but I just can't bring myself to that level of... I don't even know, the idea just disgusts me so I have the parody Star Wars sticker in democrat blue.